head - Get top rows of array or table - MATLAB (original) (raw)
Get top rows of array or table
Syntax
Description
head([A](#mw%5Fe28b3d65-d977-4985-8f5d-d5dc6ca64d94)) displays the first eight rows of array, table, or timetable A in the Command Window without storing a value.
head([A](#mw%5Fe28b3d65-d977-4985-8f5d-d5dc6ca64d94),[k](#mw%5F97cf177c-26dc-46e9-bf88-28d447ca6e91)) displays the first k rows of A.
`B` = head(___) returns the requested rows of A for either of the previous syntaxes. The data type of B is the same as the data type ofA.
Examples
Create a matrix with 100 rows, and display the first eight rows of the matrix.
If you do not specify an output argument, head does not return a value. It only displays the top of the matrix.
A = repmat((1:100)',1,4); head(A)
1 1 1 1
2 2 2 2
3 3 3 3
4 4 4 4
5 5 5 5
6 6 6 6
7 7 7 7
8 8 8 8Create a table from a file with 1468 rows.
T = readtable("outages.csv","TextType","string"); size(T)
Display the first three rows. If you do not specify an output argument, head does not return a value. It only displays the top of the table.
Region OutageTime Loss Customers RestorationTime Cause
___________ ________________ ______ __________ ________________ ______________
"SouthWest" 2002-02-01 12:18 458.98 1.8202e+06 2002-02-07 16:50 "winter storm"
"SouthEast" 2003-01-23 00:49 530.14 2.1204e+05 NaT "winter storm"
"SouthEast" 2003-02-07 21:15 289.4 1.4294e+05 2003-02-17 08:14 "winter storm"Create a table by reading data from a spreadsheet. Display the size of the table, showing that it has 1468 rows.
T = readtable("outages.csv","TextType","string"); size(T)
Return another table that has the first eight rows of T.
T2=8×6 table
Region OutageTime Loss Customers RestorationTime Cause
___________ ________________ ______ __________ ________________ _________________
"SouthWest" 2002-02-01 12:18 458.98 1.8202e+06 2002-02-07 16:50 "winter storm"
"SouthEast" 2003-01-23 00:49 530.14 2.1204e+05 NaT "winter storm"
"SouthEast" 2003-02-07 21:15 289.4 1.4294e+05 2003-02-17 08:14 "winter storm"
"West" 2004-04-06 05:44 434.81 3.4037e+05 2004-04-06 06:10 "equipment fault"
"MidWest" 2002-03-16 06:18 186.44 2.1275e+05 2002-03-18 23:23 "severe storm"
"West" 2003-06-18 02:49 0 0 2003-06-18 10:54 "attack"
"West" 2004-06-20 14:39 231.29 NaN 2004-06-20 19:16 "equipment fault"
"West" 2002-06-06 19:28 311.86 NaN 2002-06-07 00:51 "equipment fault"Input Arguments
Input data, specified as an array, cell array, table, or timetable.
Number of rows to extract, specified as a positive integer. IfA has fewer than k rows, thenhead returns all rows ofA.
Extended Capabilities
Thehead function fully supports tall arrays. For more information, see Tall Arrays.
You can use head and tail with tall arrays of any valid underlying data type (single,double, int8, datetime,table, and so on).
If you are unsure whether the result returned by gather(A) will fit in memory, then use gather(head(A)) orgather(tail(A)). These commands still fully evaluate the tall array A but return only a small subset of the result in memory.
The head function fully supports GPU arrays. To run the function on a GPU, specify the input data as a gpuArray (Parallel Computing Toolbox). For more information, see Run MATLAB Functions on a GPU (Parallel Computing Toolbox).
Version History
Introduced in R2016b
Display or return the top rows of a vector, matrix, multidimensional array, or cell array using head. In previous releases,head supports only tables, timetables, and tall arrays.
When you call head without a specified output argument,head displays the selected rows of the table but does not store the output in the ans variable. In previous releases, calling head without a specified output argument causes the output to be stored in ans.
Calling head in a live script is usually not recommended. Instead, display the table or timetable by typing the variable name with no semicolon. The Live Editor provides a widget that enables you to examine the entire table or timetable. However, if you do call head in a live script, it is recommended that you assign the output to a variable so that the live script creates a widget for the output.