PHP: Comparison - Manual (original) (raw)

Comparison Operators

Comparison operators, as their name implies, allow you to compare two values. You may also be interested in viewingthe type comparison tables, as they show examples of various type related comparisons.

Comparison Operators

Example	Name	Result
a==a == a==b	Equal	true if aisequaltoa is equal to aisequaltob after type juggling.
a===a === a===b	Identical	true if aisequaltoa is equal to aisequaltob, and they are of the same type.
a!=a != a!=b	Not equal	true if aisnotequaltoa is not equal to aisnotequaltob after type juggling.
a<>a <> a<>b	Not equal	true if aisnotequaltoa is not equal to aisnotequaltob after type juggling.
a!==a !== a!==b	Not identical	true if aisnotequaltoa is not equal to aisnotequaltob, or they are not of the same type.
a<a < a<b	Less than	true if aisstrictlylessthana is strictly less than aisstrictlylessthanb.
a>a > a>b	Greater than	true if aisstrictlygreaterthana is strictly greater than aisstrictlygreaterthanb.
a<=a <= a<=b	Less than or equal to	true if aislessthanorequaltoa is less than or equal to aislessthanorequaltob.
a>=a >= a>=b	Greater than or equal to	true if aisgreaterthanorequaltoa is greater than or equal to aisgreaterthanorequaltob.
a<=>a <=> a<=>b	Spaceship	An int less than, equal to, or greater than zero when$a is less than, equal to, or greater than$b, respectively.

If both operands arenumeric strings, or one operand is a number and the other one is anumeric string, then the comparison is done numerically. These rules also apply to theswitch statement. The type conversion does not take place when the comparison is=== or !== as this involves comparing the type as well as the value.

Warning

Prior to PHP 8.0.0, if a string is compared to a number or a numeric string then the string was converted to a number before performing the comparison. This can lead to surprising results as can be seen with the following example:

`<?php
var_dump(0 == "a");
var_dump("1" == "01");
var_dump("10" == "1e1");
var_dump(100 == "1e2");

switch (

"a") {
case 0:
echo "0";
break;
case "a":
echo "a";
break;
}
?>`

Output of the above example in PHP 7:

bool(true) bool(true) bool(true) bool(true) 0

Output of the above example in PHP 8:

bool(false) bool(true) bool(true) bool(true) a

Example #1 Comparison Operators

`<?php
// Integers
echo 1 <=> 1, ' '; // 0
echo 1 <=> 2, ' '; // -1
echo 2 <=> 1, ' '; // 1

// Floats

echo 1.5 <=> 1.5, ' '; // 0
echo 1.5 <=> 2.5, ' '; // -1
echo 2.5 <=> 1.5, ' '; // 1

// Strings

echo "a" <=> "a", ' '; // 0
echo "a" <=> "b", ' '; // -1
echo "b" <=> "a", ' '; // 1echo "a" <=> "aa", ' '; // -1
echo "zz" <=> "aa", ' '; // 1

// Arrays

echo [] <=> [], ' '; // 0
echo [1, 2, 3] <=> [1, 2, 3], ' '; // 0
echo [1, 2, 3] <=> [], ' '; // 1
echo [1, 2, 3] <=> [1, 2, 1], ' '; // 1
echo [1, 2, 3] <=> [1, 2, 4], ' '; // -1

// Objects

$a = (object) ["a" => "b"];
$b = (object) ["a" => "b"];
echo a<=>a <=> a<=>b, ' '; // 0$a = (object) ["a" => "b"];
$b = (object) ["a" => "c"];
echo a<=>a <=> a<=>b, ' '; // -1$a = (object) ["a" => "c"];
$b = (object) ["a" => "b"];
echo a<=>a <=> a<=>b, ' '; // 1

// not only values are compared; keys must match

$a = (object) ["a" => "b"];
$b = (object) ["b" => "b"];
echo a<=>a <=> a<=>b, ' '; // 1?>`

For various types, comparison is done according to the following table (in order).

Comparison with Various Types

Type of Operand 1	Type of Operand 2	Result
null or string	string	Convert null to "", numerical or lexical comparison
bool or null	anything	Convert both sides to bool, false < true
object	object	Built-in classes can define its own comparison, different classes are incomparable, same class see Object Comparison
string, resource, int or float	string, resource, int or float	Translate strings and resources to numbers, usual math
array	array	Array with fewer members is smaller, if key from operand 1 is not found in operand 2 then arrays are incomparable, otherwise - compare value by value (see following example)
object	anything	object is always greater
array	anything	array is always greater

Example #2 Boolean/null comparison

<?php // Bool and null are compared as bool always var_dump(1 == TRUE); // TRUE - same as (bool) 1 == TRUE var_dump(0 == FALSE); // TRUE - same as (bool) 0 == FALSE var_dump(100 < TRUE); // FALSE - same as (bool) 100 < TRUE var_dump(-10 < FALSE);// FALSE - same as (bool) -10 < FALSE var_dump(min(-100, -10, NULL, 10, 100)); // NULL - (bool) NULL < (bool) -100 is FALSE < TRUE ?>

Example #3 Transcription of standard array comparison

<?php // Arrays are compared like this with standard comparison operators as well as the spaceship operator. function standard_array_compare($op1, $op2) { if (count($op1) < count($op2)) { return -1; // <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>o</mi><mi>p</mi><mn>1</mn><mo><</mo></mrow><annotation encoding="application/x-tex">op1 < </annotation></semantics></math>op1<op2 } elseif (count($op1) > count($op2)) { return 1; // <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>o</mi><mi>p</mi><mn>1</mn><mo>></mo></mrow><annotation encoding="application/x-tex">op1 > </annotation></semantics></math>op1>op2 } foreach ($op1 as <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>k</mi><mi>e</mi><mi>y</mi><mo>=</mo><mo>></mo></mrow><annotation encoding="application/x-tex">key => </annotation></semantics></math>key=>val) { if (!array_key_exists($key, $op2)) { return 1; } elseif ($val < <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>o</mi><mi>p</mi><mn>2</mn><mo stretchy="false">[</mo></mrow><annotation encoding="application/x-tex">op2[</annotation></semantics></math>op2[key]) { return -1; } elseif ($val > <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>o</mi><mi>p</mi><mn>2</mn><mo stretchy="false">[</mo></mrow><annotation encoding="application/x-tex">op2[</annotation></semantics></math>op2[key]) { return 1; } } return 0; // <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>o</mi><mi>p</mi><mn>1</mn><mo>=</mo><mo>=</mo></mrow><annotation encoding="application/x-tex">op1 == </annotation></semantics></math>op1==op2 } ?>

Warning

Comparison of floating point numbers

Because of the way floats are represented internally, you should not test two floats for equality.

See the documentation for float for more information.

Note: Be aware that PHP's type juggling is not always obvious when comparing values of different types, particularly comparing ints to bools or ints to strings. It is therefore generally advisable to use === and !== comparisons rather than== and != in most cases.

Incomparable Values

While identity comparison (=== and !==) can be applied to arbitrary values, the other comparison operators should only be applied to comparable values. The result of comparing incomparable values is undefined, and should not be relied upon.

Ternary Operator

Another conditional operator is the "?:" (or ternary) operator.

Example #4 Assigning a default value

<?php // Example usage for: Ternary Operator <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>a</mi><mi>c</mi><mi>t</mi><mi>i</mi><mi>o</mi><mi>n</mi><mo>=</mo><mo stretchy="false">(</mo><mi>e</mi><mi>m</mi><mi>p</mi><mi>t</mi><mi>y</mi><mo stretchy="false">(</mo></mrow><annotation encoding="application/x-tex">action = (empty(</annotation></semantics></math>action=(empty(_POST['action'])) ? 'default' : $_POST['action'];// The above is identical to this if/else statement if (empty($_POST['action'])) { $action = 'default'; } else { <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>a</mi><mi>c</mi><mi>t</mi><mi>i</mi><mi>o</mi><mi>n</mi><mo>=</mo></mrow><annotation encoding="application/x-tex">action = </annotation></semantics></math>action=_POST['action']; } ?>

The expression (expr1) ? (expr2) : (expr3) evaluates to expr2 ifexpr1 evaluates to [true](reserved.constants.php#constant.true), andexpr3 ifexpr1 evaluates to [false](reserved.constants.php#constant.false).

It is possible to leave out the middle part of the ternary operator. Expression expr1 ?: expr3 evaluates to the result of expr1 if expr1 evaluates to [true](reserved.constants.php#constant.true), and expr3 otherwise.expr1 is only evaluated once in this case.

Note: Please note that the ternary operator is an expression, and that it doesn't evaluate to a variable, but to the result of an expression. This is important to know if you want to return a variable by reference. The statement return <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>v</mi><mi>a</mi><mi>r</mi><mo>=</mo><mo>=</mo><mn>42</mn><mo stretchy="false">?</mo></mrow><annotation encoding="application/x-tex">var == 42 ? </annotation></semantics></math>var==42?a : $b; in a return-by-reference function will therefore not work and a warning is issued.

Note:

It is recommended to avoid "stacking" ternary expressions. PHP's behaviour when using more than one unparenthesized ternary operator within a single expression is non-obvious compared to other languages. Indeed prior to PHP 8.0.0, ternary expressions were evaluated left-associative, instead of right-associative like most other programming languages. Relying on left-associativity is deprecated as of PHP 7.4.0. As of PHP 8.0.0, the ternary operator is non-associative.

Example #5 Non-obvious Ternary Behaviour

`<?php
// on first glance, the following appears to output 'true'
echo (true ? 'true' : false ? 't' : 'f');// however, the actual output of the above is 't' prior to PHP 8.0.0
// this is because ternary expressions are left-associative

// the following is a more obvious version of the same code as above

echo ((true ? 'true' : false) ? 't' : 'f');// here, one can see that the first expression is evaluated to 'true', which
// in turn evaluates to (bool) true, thus returning the true branch of the
// second ternary expression.
?>`

Note:

Chaining of short-ternaries (?:), however, is stable and behaves reasonably. It will evaluate to the first argument that evaluates to a non-falsy value. Note that undefined values will still raise a warning.

Example #6 Short-ternary chaining

<?php echo 0 ?: 1 ?: 2 ?: 3, PHP_EOL; //1 echo 0 ?: 0 ?: 2 ?: 3, PHP_EOL; //2 echo 0 ?: 0 ?: 0 ?: 3, PHP_EOL; //3 ?>

Null Coalescing Operator

Another useful shorthand operator is the "??" (or null coalescing) operator.

Example #7 Assigning a default value

<?php // Example usage for: Null Coalesce Operator <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>a</mi><mi>c</mi><mi>t</mi><mi>i</mi><mi>o</mi><mi>n</mi><mo>=</mo></mrow><annotation encoding="application/x-tex">action = </annotation></semantics></math>action=_POST['action'] ?? 'default';// The above is identical to this if/else statement if (isset($_POST['action'])) { <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>a</mi><mi>c</mi><mi>t</mi><mi>i</mi><mi>o</mi><mi>n</mi><mo>=</mo></mrow><annotation encoding="application/x-tex">action = </annotation></semantics></math>action=_POST['action']; } else { $action = 'default'; } ?>

The expression (expr1) ?? (expr2) evaluates toexpr2 if expr1 is**[null](reserved.constants.php#constant.null)**, and expr1 otherwise.

In particular, this operator does not emit a notice or warning if the left-hand side value does not exist, just like isset(). This is especially useful on array keys.

Note: Please note that the null coalescing operator is an expression, and that it doesn't evaluate to a variable, but to the result of an expression. This is important to know if you want to return a variable by reference. The statement return <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>f</mi><mi>o</mi><mi>o</mi><mo stretchy="false">?</mo><mo stretchy="false">?</mo></mrow><annotation encoding="application/x-tex">foo ?? </annotation></semantics></math>foo??bar; in a return-by-reference function will therefore not work and a warning is issued.

Note:

The null coalescing operator has low precedence. That means if mixing it with other operators (such as string concatenation or arithmetic operators) parentheses will likely be required.

<?php // Raises a warning that $name is undefined. print 'Mr. ' . $name ?? 'Anonymous';// Prints "Mr. Anonymous" print 'Mr. ' . ($name ?? 'Anonymous'); ?>

Note:

Please note that the null coalescing operator allows for simple nesting:

Example #8 Nesting null coalescing operator

`<?php

$foo

= null;
$bar = null;
$baz = 1;
$qux = 2;

echo

foo??foo ?? foo??bar ?? baz??baz ?? baz??qux; // outputs 1?>`

Found A Problem?

crazy888s at hotmail dot com ¶

15 years ago

I couldn't find much info on stacking the new ternary operator, so I ran some tests:

<?php
echo 0 ?: 1 ?: 2 ?: 3; //1
echo 1 ?: 0 ?: 3 ?: 2; //1
echo 2 ?: 1 ?: 0 ?: 3; //2
echo 3 ?: 2 ?: 1 ?: 0; //3

echo 0 ?: 1 ?: 2 ?: 3; //1
echo 0 ?: 0 ?: 2 ?: 3; //2
echo 0 ?: 0 ?: 0 ?: 3; //3
?>

It works just as expected, returning the first non-false value within a group of expressions.

Tahazzot ¶

4 years ago

Very careful when reading PHP documentation, Here's a lot of miss information. 

According to documentation, They say's (int) 0 == (string) "a" is true. But it is not in PHP 8.

var_dump(0 == "a"); // 0 == 0 -> true

Now In PHP 8 it's False.

gfilippakis at sleed dot gr ¶

2 years ago

Please note that using the null coalescing operator to check properties on a class that has the __get magic method (without an __isset magic method) invokes the magic method. 

For example:

<?php

class A
{
    public function __get($property)
    {
        echo 'Called __get for ' . $property . PHP_EOL;
    }
}

$a = new A();

echo 'Trying null coalescing operator' . PHP_EOL; <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>b</mi><mo>=</mo></mrow><annotation encoding="application/x-tex">b = </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6944em;"></span><span class="mord mathnormal">b</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span></span></span></span>a->test ?? 5;

echo 'Trying isset()' . PHP_EOL;
if (isset($a->test)) {
    <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>b</mi><mo>=</mo></mrow><annotation encoding="application/x-tex">b = </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6944em;"></span><span class="mord mathnormal">b</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span></span></span></span>a->test;
} else {
    $b = 5;
}

?>

adam at caucho dot com ¶

19 years ago

Note: according to the spec, PHP's comparison operators are not transitive.  For example, the following are all true in PHP5:

"11" < "a" < 2 < "11"

As a result, the outcome of sorting an array depends on the order the elements appear in the pre-sort array.  The following code will dump out two arrays with *different* orderings:

<?php
$a = array(2,    "a",  "11", 2);
$b = array(2,    "11", "a",  2);
sort($a);
var_dump($a);
sort($b);
var_dump($b);
?>

This is not a bug report -- given the spec on this documentation page, what PHP does is "correct".  But that may not be what was intended...

rshawiii at yahoo dot com ¶

19 years ago

You can't just compare two arrays with the === operator
like you would think to find out if they are equal or not.  This is more complicated when you have multi-dimensional arrays.  Here is a recursive comparison function.

<?php
/**
 * Compares two arrays to see if they contain the same values.  Returns TRUE or FALSE.
 * usefull for determining if a record or block of data was modified (perhaps by user input)
 * prior to setting a "date_last_updated" or skipping updating the db in the case of no change.
 *
 * @param array $a1
 * @param array $a2
 * @return boolean
 */
function array_compare_recursive($a1, $a2)
{
   if (!(is_array($a1) and (is_array($a2)))) { return FALSE;}    
    
   if (!count($a1) == count($a2)) 
      {
       return FALSE; // arrays don't have same number of entries
      }
      
   foreach ($a1 as <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>k</mi><mi>e</mi><mi>y</mi><mo>=</mo><mo>&gt;</mo></mrow><annotation encoding="application/x-tex">key =&gt; </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.8889em;vertical-align:-0.1944em;"></span><span class="mord mathnormal" style="margin-right:0.03148em;">k</span><span class="mord mathnormal" style="margin-right:0.03588em;">ey</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=&gt;</span></span></span></span>val) 
   {
       if (!array_key_exists($key, $a2)) 
           {return FALSE; // uncomparable array keys don't match
              } 
       elseif (is_array($val) and is_array($a2[$key]))  // if both entries are arrays then compare recursive 
           {if (!array_compare_recursive($val,$a2[$key])) return FALSE;
           } 
       elseif (!($val === <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>a</mi><mn>2</mn><mo stretchy="false">[</mo></mrow><annotation encoding="application/x-tex">a2[</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mord mathnormal">a</span><span class="mord">2</span><span class="mopen">[</span></span></span></span>key])) // compare entries must be of same type.
           {return FALSE;
           }
   }
   return TRUE; // <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>a</mi><mn>1</mn><mo>=</mo><mo>=</mo><mo>=</mo></mrow><annotation encoding="application/x-tex">a1 === </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6444em;"></span><span class="mord mathnormal">a</span><span class="mord">1</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">===</span></span></span></span>a2
}
?>

Sumon Mahmud ¶

5 years ago

Extending from here: https://www.php.net/manual/en/language.operators.comparison.php#121907

$a = ['a' => 1, 'b' => 2, 'c' => 3, 'e' => 4]; 
$b = ['a' => 1, 'b' => 2, 'd' => 3, 'e' => 4];

echo <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>a</mi><mo>&gt;</mo></mrow><annotation encoding="application/x-tex">a &gt; </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.5782em;vertical-align:-0.0391em;"></span><span class="mord mathnormal">a</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">&gt;</span></span></span></span>b; // 0
echo <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>b</mi><mo>&gt;</mo></mrow><annotation encoding="application/x-tex">b &gt; </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.7335em;vertical-align:-0.0391em;"></span><span class="mord mathnormal">b</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">&gt;</span></span></span></span>a; // 0
echo <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>a</mi><mo>&lt;</mo></mrow><annotation encoding="application/x-tex">a &lt;</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.5782em;vertical-align:-0.0391em;"></span><span class="mord mathnormal">a</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">&lt;</span></span></span></span>b; // 0
echo <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>b</mi><mo>&lt;</mo></mrow><annotation encoding="application/x-tex">b &lt; </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.7335em;vertical-align:-0.0391em;"></span><span class="mord mathnormal">b</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">&lt;</span></span></span></span>a; // 0

If using spaceship operator then it is returning true like : 

echo <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>a</mi><mo>&lt;</mo><mo>=</mo><mo>&gt;</mo></mrow><annotation encoding="application/x-tex">a &lt;=&gt; </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.5782em;vertical-align:-0.0391em;"></span><span class="mord mathnormal">a</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">&lt;=&gt;</span></span></span></span>b; //1
echo <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>b</mi><mo>&lt;</mo><mo>=</mo><mo>&gt;</mo></mrow><annotation encoding="application/x-tex">b &lt;=&gt; </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.7335em;vertical-align:-0.0391em;"></span><span class="mord mathnormal">b</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">&lt;=&gt;</span></span></span></span>a; //1
echo <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>a</mi><mo>&lt;</mo><mo>=</mo><mo>&gt;</mo></mrow><annotation encoding="application/x-tex">a &lt;=&gt; </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.5782em;vertical-align:-0.0391em;"></span><span class="mord mathnormal">a</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">&lt;=&gt;</span></span></span></span>b; //1
echo <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>b</mi><mo>&lt;</mo><mo>=</mo><mo>&gt;</mo></mrow><annotation encoding="application/x-tex">b &lt;=&gt; </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.7335em;vertical-align:-0.0391em;"></span><span class="mord mathnormal">b</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">&lt;=&gt;</span></span></span></span>a; //1

bishop ¶

19 years ago

When you want to know if two arrays contain the same values, regardless of the values' order, you cannot use "==" or "===".  In other words:

<?php
(array(1,2) == array(2,1)) === false;
?>

To answer that question, use:

<?php
function array_equal($a, $b) {
    return (is_array($a) && is_array($b) && array_diff($a, <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>b</mi><mo stretchy="false">)</mo><mo>=</mo><mo>=</mo><mo>=</mo><mi>a</mi><mi>r</mi><mi>r</mi><mi>a</mi><msub><mi>y</mi><mi>d</mi></msub><mi>i</mi><mi>f</mi><mi>f</mi><mo stretchy="false">(</mo></mrow><annotation encoding="application/x-tex">b) === array_diff(</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mord mathnormal">b</span><span class="mclose">)</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">===</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mord mathnormal">a</span><span class="mord mathnormal" style="margin-right:0.02778em;">rr</span><span class="mord mathnormal">a</span><span class="mord"><span class="mord mathnormal" style="margin-right:0.03588em;">y</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.3361em;"><span style="top:-2.55em;margin-left:-0.0359em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight">d</span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.15em;"><span></span></span></span></span></span></span><span class="mord mathnormal">i</span><span class="mord mathnormal" style="margin-right:0.10764em;">ff</span><span class="mopen">(</span></span></span></span>b, $a));
}
?>

A related, but more strict problem, is if you need to ensure that two arrays contain the same key=>value pairs, regardless of the order of the pairs.  In that case, use:

<?php
function array_identical($a, $b) {
    return (is_array($a) && is_array($b) && array_diff_assoc($a, <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>b</mi><mo stretchy="false">)</mo><mo>=</mo><mo>=</mo><mo>=</mo><mi>a</mi><mi>r</mi><mi>r</mi><mi>a</mi><msub><mi>y</mi><mi>d</mi></msub><mi>i</mi><mi>f</mi><msub><mi>f</mi><mi>a</mi></msub><mi>s</mi><mi>s</mi><mi>o</mi><mi>c</mi><mo stretchy="false">(</mo></mrow><annotation encoding="application/x-tex">b) === array_diff_assoc(</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mord mathnormal">b</span><span class="mclose">)</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">===</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mord mathnormal">a</span><span class="mord mathnormal" style="margin-right:0.02778em;">rr</span><span class="mord mathnormal">a</span><span class="mord"><span class="mord mathnormal" style="margin-right:0.03588em;">y</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.3361em;"><span style="top:-2.55em;margin-left:-0.0359em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight">d</span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.15em;"><span></span></span></span></span></span></span><span class="mord mathnormal">i</span><span class="mord mathnormal" style="margin-right:0.10764em;">f</span><span class="mord"><span class="mord mathnormal" style="margin-right:0.10764em;">f</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.1514em;"><span style="top:-2.55em;margin-left:-0.1076em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight">a</span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.15em;"><span></span></span></span></span></span></span><span class="mord mathnormal">ssoc</span><span class="mopen">(</span></span></span></span>b, $a));
}
?>

Example:
<?php
$a = array (2, 1);
$b = array (1, 2);
// true === array_equal($a, $b);
// false === array_identical($a, $b);

$a = array ('a' => 2, 'b' => 1);
$b = array ('b' => 1, 'a' => 2);
// true === array_identical($a, $b)
// true === array_equal($a, $b)
?>

(See also the solution "rshawiii at yahoo dot com" posted)

admin at zeros dot co dot id ¶

3 years ago

Please be careful when you try to compare strings that have a plus sign `+` at the beginning (such as phone number, etc). When you use the Equal operator `==` PHP will ignore the plus sign. Use Identical operator `===` instead

Example:

$str1 = "62";
$str2 = "+62";

var_dump($str1 == $str2); // bool(true)
var_dump($str1 === $str2); // bool(false)

Hayley Watson ¶

2 years ago

Between the "shortcut ternary" (aka "elvis") and "spaceship" operators, you can write some quite compact comparison functions for usort and its ilk.

If you want to sort an array of associative arrays by several different keys you can chain them in the same way that you can list column names in an SQL ORDER BY clause.

<?php
usort($array, fn($a, <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>b</mi><mo stretchy="false">)</mo><mo>=</mo><mo>&gt;</mo></mrow><annotation encoding="application/x-tex">b) =&gt; </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mord mathnormal">b</span><span class="mclose">)</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=&gt;</span></span></span></span>a['a'] <=> $b['a']
                         ?: <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>b</mi><msup><mo stretchy="false">[</mo><mo mathvariant="normal" lspace="0em" rspace="0em">′</mo></msup><msup><mi>b</mi><mo mathvariant="normal" lspace="0em" rspace="0em">′</mo></msup><mo stretchy="false">]</mo><mo>&lt;</mo><mo>=</mo><mo>&gt;</mo></mrow><annotation encoding="application/x-tex">b[&#x27;b&#x27;] &lt;=&gt; </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:1.0019em;vertical-align:-0.25em;"></span><span class="mord mathnormal">b</span><span class="mopen"><span class="mopen">[</span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:0.7519em;"><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mord mtight">′</span></span></span></span></span></span></span></span></span><span class="mord"><span class="mord mathnormal">b</span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:0.7519em;"><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mord mtight">′</span></span></span></span></span></span></span></span></span><span class="mclose">]</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">&lt;=&gt;</span></span></span></span>a['b']
                         ?: <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>a</mi><msup><mo stretchy="false">[</mo><mo mathvariant="normal" lspace="0em" rspace="0em">′</mo></msup><msup><mi>c</mi><mo mathvariant="normal" lspace="0em" rspace="0em">′</mo></msup><mo stretchy="false">]</mo><mo>&lt;</mo><mo>=</mo><mo>&gt;</mo></mrow><annotation encoding="application/x-tex">a[&#x27;c&#x27;] &lt;=&gt; </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:1.0019em;vertical-align:-0.25em;"></span><span class="mord mathnormal">a</span><span class="mopen"><span class="mopen">[</span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:0.7519em;"><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mord mtight">′</span></span></span></span></span></span></span></span></span><span class="mord"><span class="mord mathnormal">c</span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:0.7519em;"><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mord mtight">′</span></span></span></span></span></span></span></span></span><span class="mclose">]</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">&lt;=&gt;</span></span></span></span>b['c']);
?>
Will sort the array by column 'a', then by column 'b' descending, then by column 'c'; or in SQL-speak 'ORDER BY a, b DESC, c".

Ryan Mott ¶

6 years ago

Searching for "double question mark" operator should find this page (and hopefully after this comment the crawlers will agree)

niall at maranelda dot org ¶

8 years ago

Care must be taken when using the spaceship operator with arrays that do not have the same keys:

- Contrary to the notes above ("Example #2 Transcription of standard array comparison"), it does *not* return null if the left-hand array contains a key that the right-hand array does not.
- Because of this, the result depends on the order you do the comparison in.

For example:

<?php
$a = ['a' => 1, 'b' => 2, 'c' => 3, 'e' => 4];
$b = ['a' => 1, 'b' => 2, 'd' => 3, 'e' => 4];

var_dump($a <=> <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>b</mi><mo stretchy="false">)</mo><mo separator="true">;</mo><mi mathvariant="normal">/</mi><mi mathvariant="normal">/</mi><mi>i</mi><mi>n</mi><mi>t</mi><mo stretchy="false">(</mo><mn>1</mn><mo stretchy="false">)</mo><mo>:</mo></mrow><annotation encoding="application/x-tex">b);        // int(1) : </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mord mathnormal">b</span><span class="mclose">)</span><span class="mpunct">;</span><span class="mspace" style="margin-right:0.1667em;"></span><span class="mord">//</span><span class="mord mathnormal">in</span><span class="mord mathnormal">t</span><span class="mopen">(</span><span class="mord">1</span><span class="mclose">)</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">:</span></span></span></span>a > <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>b</mi><mi>b</mi><mi>e</mi><mi>c</mi><mi>a</mi><mi>u</mi><mi>s</mi><mi>e</mi></mrow><annotation encoding="application/x-tex">b because </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6944em;"></span><span class="mord mathnormal">bb</span><span class="mord mathnormal">ec</span><span class="mord mathnormal">a</span><span class="mord mathnormal">u</span><span class="mord mathnormal">se</span></span></span></span>a has the 'c' key and $b doesn't.

var_dump($b <=> <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>a</mi><mo stretchy="false">)</mo><mo separator="true">;</mo><mi mathvariant="normal">/</mi><mi mathvariant="normal">/</mi><mi>i</mi><mi>n</mi><mi>t</mi><mo stretchy="false">(</mo><mn>1</mn><mo stretchy="false">)</mo><mo>:</mo></mrow><annotation encoding="application/x-tex">a);        // int(1) : </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mord mathnormal">a</span><span class="mclose">)</span><span class="mpunct">;</span><span class="mspace" style="margin-right:0.1667em;"></span><span class="mord">//</span><span class="mord mathnormal">in</span><span class="mord mathnormal">t</span><span class="mopen">(</span><span class="mord">1</span><span class="mclose">)</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">:</span></span></span></span>b > <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>a</mi><mi>b</mi><mi>e</mi><mi>c</mi><mi>a</mi><mi>u</mi><mi>s</mi><mi>e</mi></mrow><annotation encoding="application/x-tex">a because </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6944em;"></span><span class="mord mathnormal">ab</span><span class="mord mathnormal">ec</span><span class="mord mathnormal">a</span><span class="mord mathnormal">u</span><span class="mord mathnormal">se</span></span></span></span>b has the 'd' key and $a doesn't.
?>

Cuong Huy To ¶

14 years ago

In the table "Comparison with Various Types", please move the last line about "Object" to be above the line about "Array", since Object is considered to be greater than Array (tested on 5.3.3)

(Please remove my "Anonymous" post of the same content before. You could check IP to see that I forgot to type my name)

Marcin Kuzawiski ¶

10 years ago

A < B and still B < A...

$A = [1 => 1, 2 => 0, 3 => 1];
$B = [1 => 1, 3 => 0, 2 => 1];

var_dump($A < $B);  // TRUE
var_dump($B < $A);  // TRUE

var_dump($A > $B);  // TRUE
var_dump($B > $A);  // TRUE

Next - C and D are comparable, but neither C < D nor D < C (and still C != D)...

$C = [1 => 1, 2 => 1, 3 => 0];
$D = [1 => 1, 3 => 1, 2 => 0];

var_dump($C < $D); // FALSE
var_dump($D < $C); // FALSE

var_dump($C > $D); // FALSE
var_dump($D > $C); // FALSE

var_dump($D == $C); // FALSE

billynoah at gmail dot com ¶

10 months ago

It's worth noting that there can be a difference in the logical operation of shorthand ternary (expr1 ?: expr2) vs the full version (expr1 ? expr1 : expr2). The shorthand style may also offer a slight performance enhancement because the initial expression will only be evaluated once.

Example:
<?php
// my_func() will be called twice here
// additionally, my_func() may not return the same value both times!
$var = my_func() ? my_func() : false;

// my_func() will only be called once here
$var = my_func() ?: false;