size

Array size

Syntax

sz = size(A)

szdim = size(A,dim)

szdim = size(A,dim1,dim2,...,dimN)

[sz1,...,szN] = size(___)

Description

sz = size(A) returns a row vector whose elements are the lengths of the corresponding dimensions of A. For example, if A is a 3-by-4 matrix, then size(A) returns the vector [3 4].

If A is a table or timetable, then size(A) returns a two-element row vector consisting of the number of rows and the number of table variables.

szdim = size(A,dim) returns the length of dimension dim when dim is a positive integer scalar. You can also specify dim as a vector of positive integers to query multiple dimension lengths at a time. For example, size(A,[2 3]) returns the lengths of the second and third dimensions of A in the 1-by-2 row vector szdim.

szdim = size(A,dim1,dim2,...,dimN) returns the lengths of dimensions dim1,dim2,...,dimN in the row vector szdim.

[sz1,...,szN] = size(___) returns the lengths of the queried dimensions of A separately.

Examples

Size of 4-D Array

Create a random 4-D array and return its size.

A = rand(2,3,4,5);
sz = size(A)

sz = 1×4

     2     3     4     5

Query the length of the second dimension of A.

szdim2 = size(A,2)

szdim2 = 
3

Query the length of the last dimension of A.

szdimlast = size(A,ndims(A))

szdimlast = 
5

You can query multiple dimension lengths at a time by specifying a vector dimension argument. For example, find the lengths of the first and third dimensions of A.

szdim13 = size(A,[1 3])

szdim13 = 1×2

     2     4

Find the lengths of the second through fourth dimensions of A.

szdim23 = size(A,2:4)

szdim23 = 1×3

     3     4     5

Alternatively, you can list the queried dimensions as separate input arguments.

szdim23 = size(A,2,3,4);

Size of Table

Create a table with 5 rows and 4 variables.

LastName = {'Smith';'Johnson';'Williams';'Jones';'Brown'};
Age = [38;43;38;40;49];
Height = [71;69;64;67;64];
Weight = [176;163;131;133;119];
BloodPressure = [124 93; 109 77; 125 83; 117 75; 122 80];

A = table(Age,Height,Weight,BloodPressure,'RowNames',LastName)

A=5×4 table
                Age    Height    Weight    BloodPressure
                ___    ______    ______    _____________

    Smith       38       71       176       124     93  
    Johnson     43       69       163       109     77  
    Williams    38       64       131       125     83  
    Jones       40       67       133       117     75  
    Brown       49       64       119       122     80  

Find the size of the table. Although the BloodPressure variable contains two columns, size only counts the number of variables.

sz = size(A)

sz = 1×2

     5     4

Dimension Lengths as Separate Arguments

Create a random matrix and return the number of rows and columns separately.

A = rand(4,3);
[numRows,numCols] = size(A)

numRows = 
4

numCols = 
3

Input Arguments

A — Input array

scalar | vector | matrix | multidimensional array

Input array, specified as a scalar, a vector, a matrix, or a multidimensional array.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | logical | char | string | struct | function_handle | cell | categorical | datetime | duration | calendarDuration | table | timetable

Complex Number Support: Yes

dim — Queried dimensions

positive integer scalar | vector of positive integer scalars | empty array

Queried dimensions, specified as a positive integer scalar, a vector of positive integer scalars, or an empty array of size 0-by-0, 0-by-1, or 1-by-0. If an element of dim is larger than ndims(A), then size returns 1 in the corresponding element of the output. If dim is an empty array, then size returns a 1-by-0 empty array.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

dim1,dim2,...,dimN — List of queried dimensions

positive integer scalars

List of queried dimensions, specified as positive integer scalars separated by commas. If an element of the list is larger than ndims(A), then size returns 1 in the corresponding element of the output.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

Output Arguments

sz — Array size

row vector of nonnegative integers

Array size, returned as a row vector of nonnegative integers.

• Each element of sz represents the length of the corresponding dimension of A. If any element of sz is equal to 0, then A is an empty array.

• If A is a scalar, then sz is the row vector [1 1].

• If A is a table or timetable, then sz is a two-element row vector containing the number of rows and the number of variables. Multiple columns within a single variable are not counted.

• If A is a character vector of type char, then size returns the row vector [1 M] where M is the number of characters. However, if A is a string scalar, size returns [1 1] because it is a single element of a string array. For example, compare the output of size for a character vector and string:

  szchar = size('mytext')

  szchar =
  
       1     6

  szstr = size("mytext")

  szstr =
  
       1     1
  

  To find the number of characters in a string, use the strlength function.

Data Types: double

szdim — Dimension lengths

nonnegative integer scalar | vector of nonnegative integer scalars | 1-by-0 empty array

Dimension lengths, returned as a nonnegative integer scalar when dim is a positive integer scalar, a row vector of nonnegative integer scalars when dim is a vector of positive integers, or a 1-by-0 empty array when dim is an empty array. If an element of the specified dimension argument is larger than ndims(A), then size returns 1 in the corresponding element of szdim.

Data Types: double

sz1,...,szN — Dimension lengths listed separately

nonnegative integer scalars

Dimension lengths listed separately, returned as nonnegative integer scalars separated by commas.

• When dim is not specified and fewer than ndims(A) output arguments are listed, then all remaining dimension lengths are collapsed into the last argument in the list. For example, if A is a 3-D array with size [3 4 5], then [sz1,sz2] = size(A) returns sz1 = 3 and sz2 = 20.

• When dim is specified, the number of output arguments must equal the number of queried dimensions.

• If you specify more than ndims(A) output arguments, then the extra trailing arguments are returned as 1.

Data Types: double

Tips

• To determine if an array is empty, a scalar, or a matrix, use the functions isempty, isscalar, and ismatrix. You can also determine the orientation of a vector with the isrow and iscolumn functions.

Extended Capabilities

Tall Arrays

Calculate with arrays that have more rows than fit in memory.

The size function fully supports tall arrays. For more information, see Tall Arrays.

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

• For variable-size N-D arrays, the size function can return a different result in the generated code than in MATLAB^®. See Incompatibility with MATLAB in Determining Size of Variable-Size N-D Arrays (MATLAB Coder).

GPU Code Generation
Generate CUDA® code for NVIDIA® GPUs using GPU Coder™.

HDL Code Generation
Generate VHDL, Verilog and SystemVerilog code for FPGA and ASIC designs using HDL Coder™.

Thread-Based Environment

Run code in the background using MATLAB® backgroundPool or accelerate code with Parallel Computing Toolbox™ ThreadPool.

This function fully supports thread-based environments. For more information, see Run MATLAB Functions in Thread-Based Environment.

GPU Arrays

Accelerate code by running on a graphics processing unit (GPU) using Parallel Computing Toolbox™.

The size 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).

Distributed Arrays

Partition large arrays across the combined memory of your cluster using Parallel Computing Toolbox™.

This function fully supports distributed arrays. For more information, see Run MATLAB Functions with Distributed Arrays (Parallel Computing Toolbox).

Version History

Introduced before R2006a

R2019b: Specify dimensions as vector of positive integers or separate input arguments

You can specify dim as a vector of positive integers to query multiple dimension lengths at a time. Alternatively, you can list the queried dimensions as separate input arguments dim1,dim2,...,dimN. For an example, see Size of 4-D Array.