union - Union of two sets of data - MATLAB (original) (raw)

Union of two sets of data

Syntax

Description

[C](#btcme1c-1-C) = union([A,B](#btcme1c-1%5Fsep%5Fshared-AB)) returns the combined data from A and B with no repetitions. C is in sorted order.

example

[C](#btcme1c-1-C) = union([A,B](#btcme1c-1%5Fsep%5Fshared-AB),[setOrder](#btcme1c-1-setOrder)) returns C in a specific order. setOrder can be 'sorted' or 'stable'.

example

[C](#btcme1c-1-C) = union([A,B](#btcme1c-1%5Fsep%5Fshared-AB),___,'rows') and`C` = union(`A,B`,'rows',___) treat each row of A and each row of B as single entities and return the combined rows from A andB, with no repetitions. You must specifyA and B and optionally can specifysetOrder.

The 'rows' option does not support cell arrays, unless one of the inputs is either a categorical array or a datetime array.

[[C](#btcme1c-1-C),[ia](#btcme1c-1-ia),[ib](#btcme1c-1-ib)] = union(___) also returns index vectors ia and ib using any of the previous syntaxes.

example

[[C](#btcme1c-1-C),[ia](#btcme1c-1-ia),[ib](#btcme1c-1-ib)] = union([A,B](#btcme1c-1%5Fsep%5Fshared-AB),'legacy') and[`C`,`ia`,`ib`] = union(`A,B`,'rows','legacy') preserve the behavior of the union function from R2012b and prior releases.

The 'legacy' option does not support categorical arrays, datetime arrays, duration arrays, tables, or timetables.

example

Examples

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Define two vectors with a value in common.

A = [5 7 1]; B = [3 1 1];

Find the union of vectors A and B.

Define two tables with rows in common.

A = table([1:5]',['A';'B';'C';'D';'E'],logical([0;1;0;1;0]))

A=5×3 table Var1 Var2 Var3 ____ ____ _____

 1       A      false
 2       B      true 
 3       C      false
 4       D      true 
 5       E      false

B = table([1:2:10]',['A';'C';'E';'G';'I'],logical(zeros(5,1)))

B=5×3 table Var1 Var2 Var3 ____ ____ _____

 1       A      false
 3       C      false
 5       E      false
 7       G      false
 9       I      false

Find the union of tables A and B.

C=7×3 table Var1 Var2 Var3 ____ ____ _____

 1       A      false
 2       B      true 
 3       C      false
 4       D      true 
 5       E      false
 7       G      false
 9       I      false

Define two vectors with a value in common.

A = [5 7 1]; B = [3 1 1];

Find the union of vectors A and B, as well as the index vectors, ia and ib.

The values in C are the combined values of A(ia) and B(ib).

Define a table, A, of gender, age, and height for three people.

A = table(['M';'M';'F'],[27;52;31],[74;68;64],... 'VariableNames',{'Gender' 'Age' 'Height'},... 'RowNames',{'Ted' 'Fred' 'Betty'})

A=3×3 table Gender Age Height ______ ___ ______

Ted        M       27       74  
Fred       M       52       68  
Betty      F       31       64

Define a table, B with the same variables as A.

B = table(['F';'M'],[64;68],[31;47],... 'VariableNames',{'Gender' 'Height' 'Age'},... 'RowNames',{'Meg' 'Joe'})

B=2×3 table Gender Height Age ______ ______ ___

Meg      F         64      31 
Joe      M         68      47

Find the union of tables A and B, as well as the index vectors, ia and ib.

C=4×3 table Gender Age Height ______ ___ ______

Betty      F       31       64  
Ted        M       27       74  
Joe        M       47       68  
Fred       M       52       68

The data for Meg and Betty are the same. union only returns the index from A, which corresponds to Betty.

Define two matrices with a row in common.

A = [2 2 2; 0 0 1]; B = [1 2 3; 2 2 2; 2 2 2];

Find the combined rows of A and B, with no repetition, as well as the index vectors ia and ib.

[C,ia,ib] = union(A,B,'rows')

C = 3×3

 0     0     1
 1     2     3
 2     2     2

The rows of C are the combined rows of A(ia,:) and B(ib,:).

Use the setOrder argument to specify the ordering of the values in C.

Specify 'stable' if you want the values in C to have the same order as in A and B.

A = [5 7 1]; B = [3 1 1]; [C,ia,ib] = union(A,B,'stable')

Alternatively, you can specify 'sorted' order.

A = [5 7 1]; B = [3 1 1]; [C,ia,ib] = union(A,B,'sorted')

Define two vectors containing NaN.

A = [5 NaN 1]; B = [4 NaN NaN];

Find the union of vectors A and B.

C = 1×6

 1     4     5   NaN   NaN   NaN

union treats NaN values as distinct.

Create a cell array of character vectors, A.

A = {'dog','cat','fish','horse'};

Create a cell array of character vectors, B, where some of the vectors have trailing white space.

B = {'dog ','cat','fish ','horse'};

Combine the elements of A and B.

C = 1×6 cell {'cat'} {'dog'} {'dog '} {'fish'} {'fish '} {'horse'}

union treats trailing white space in cell arrays of character vectors as distinct characters.

Create a column vector character array.

A = 3×1 char array 'A' 'B' 'C'

Create a row vector containing elements of numeric type double.

The union of A and B returns a column vector character array.

C = 6×1 char array 'A' 'B' 'C' 'D' 'E' 'F'

Create a character vector containing the letters a , b, and c.

A = ['a';'b';'c']; class(A)

Create a cell array of character vectors containing the letters c, d, and e.

B = {'c','d','e'}; class(B)

Combine the elements of A and B.

C = 5×1 cell {'a'} {'b'} {'c'} {'d'} {'e'}

The result, C, is a cell array of character vectors.

Use the 'legacy' flag to preserve the behavior of union from R2012b and prior releases in your code.

Find the union of A and B with the current behavior.

A = [5 7 1]; B = [3 1 1]; [C1,ia1,ib1] = union(A,B)

Find the union of A and B, and preserve the legacy behavior.

A = [5 7 1]; B = [3 1 1]; [C2,ia2,ib2] = union(A,B,'legacy')

Input Arguments

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Order flag, specified as 'sorted' or'stable', indicates the order of the values (or rows) in C.

Flag Description
'sorted' The values (or rows) in C return in sorted order as returned by sort.ExampleC = union([5 5 3],[1 2 5],'sorted')C = 1 2 3 5
'stable' The values (or rows) in C return in the same order as they appear inA, thenB.ExampleC = union([5 5 3],[1 2 5],'stable')C = 5 3 1 2

Data Types: char | string

Output Arguments

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Combined data of A and B, returned as a vector, matrix, table, or timetable. If the inputs A and B are tables or timetables, then the order of the variables in C is the same as the order of the variables in A.

The following describes the shape of C when the inputs are vectors or matrices and when the 'legacy' flag is not specified:

The class of the inputs A and B determines the class of C:

Index to A, returned as a column vector when the'legacy' flag is not specified. ia indicates the values (or rows) in A that contribute to the union. If a value (or row) appears multiple times inA, then ia contains the index to the first occurrence of the value (or row). If a value appears in bothA and B, thenia contains the index to the first occurrence inA.

Index to B, returned as a column vector when the'legacy' flag is not specified. ib indicates the values (or rows) in B that contribute to the union. If there is a repeated value (or row) appearing exclusively inB, then ib contains the index to the first occurrence of the value. If a value (or row) appears in bothA and B, thenib does not contain an index to the value (or row).

Tips

Extended Capabilities

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Theunion function supports tall arrays with the following usage notes and limitations:

For more information, see Tall Arrays.

Usage notes and limitations:

The union function supports GPU array input with these usage notes and limitations:

For more information, see Run MATLAB Functions on a GPU (Parallel Computing Toolbox).

Usage notes and limitations:

For more information, see Run MATLAB Functions with Distributed Arrays (Parallel Computing Toolbox).

Version History

Introduced before R2006a