repmat - Repeat copies of array - MATLAB (original) (raw)

Syntax

Description

B = repmat([A](#btzavfc-1-A),[n](#btzavfc-1-n)) returns an array containing n copies of A in the row and column dimensions. The size of B is size(A)*n when A is a matrix.

example

B = repmat([A](#btzavfc-1-A),[r1,...,rN](#btzavfc-1-r1rN)) specifies a list of scalars, r1,..,rN, that describes how copies of A are arranged in each dimension. When A has N dimensions, the size of B is size(A).*[r1...rN]. For example, repmat([1 2; 3 4],2,3) returns a 4-by-6 matrix.

example

B = repmat([A](#btzavfc-1-A),[r](#btzavfc-1-r)) specifies the repetition scheme with row vector r. For example, repmat(A,[2 3]) returns the same result as repmat(A,2,3).

example

Examples

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Create a 3-by-2 matrix whose elements contain the value 10.

A = 3×2

10    10
10    10
10    10

Repeat copies of a matrix into a 2-by-2 block arrangement.

A = 3×3

100 0 0 0 200 0 0 0 300

B = 6×6

100 0 0 100 0 0 0 200 0 0 200 0 0 0 300 0 0 300 100 0 0 100 0 0 0 200 0 0 200 0 0 0 300 0 0 300

Repeat copies of a matrix into a 2-by-3 block arrangement.

A = 3×3

100 0 0 0 200 0 0 0 300

B = 6×9

100 0 0 100 0 0 100 0 0 0 200 0 0 200 0 0 200 0 0 0 300 0 0 300 0 0 300 100 0 0 100 0 0 100 0 0 0 200 0 0 200 0 0 200 0 0 0 300 0 0 300 0 0 300

Repeat copies of a matrix into a 2-by-3-by-2 block arrangement.

B = B(:,:,1) =

 1     2     1     2     1     2
 3     4     3     4     3     4
 1     2     1     2     1     2
 3     4     3     4     3     4

B(:,:,2) =

 1     2     1     2     1     2
 3     4     3     4     3     4
 1     2     1     2     1     2
 3     4     3     4     3     4

Vertically stack a row vector four times.

A = 1:4; B = repmat(A,4,1)

B = 4×4

 1     2     3     4
 1     2     3     4
 1     2     3     4
 1     2     3     4

Horizontally stack a column vector four times.

A = (1:3)';
B = repmat(A,1,4)

B = 3×4

 1     1     1     1
 2     2     2     2
 3     3     3     3

Create a table with variables Age and Height.

A = table([39; 26],[70; 63],'VariableNames',{'Age' 'Height'})

A=2×2 table Age Height ___ ______

39       70  
26       63  

Repeat copies of the table into a 2-by-3 block format.

B=4×6 table Age Height Age_1 Height_1 Age_2 Height_2 ___ ______ _____ ________ _____ ________

39       70       39         70        39         70   
26       63       26         63        26         63   
39       70       39         70        39         70   
26       63       26         63        26         63   

repmat repeats the entries of the table and appends a number to the new variable names.

Create two column vectors.

A = [1; 3; 5]; B = [2; 4];

Generate all element combinations of the two vectors by using repelem and repmat. Each row of the output T is a combination with the first element coming from the first vector and the second element coming from the second vector. This command is equivalent to finding the Cartesian product of two vectors.

T = [repelem(A,numel(B)) repmat(B,numel(A),1)]

T = 6×2

 1     2
 1     4
 3     2
 3     4
 5     2
 5     4

Starting in R2023a, you can also use the combinations function to generate all element combinations of two vectors.

T=6×2 table A B _ _

1    2
1    4
3    2
3    4
5    2
5    4

Input Arguments

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

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

Number of times to repeat the input array in the row and column dimensions, specified as an integer value. If n is 0 or negative, the result is an empty array.

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

Repetition factors for each dimension, specified as separate arguments of integer values. If any repetition factor is 0 or negative, the result is an empty array.

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

Vector of repetition factors for each dimension, specified as a row vector of integer values. If any value in r is 0 or negative, the result is an empty array.

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

Tips

• To build block arrays by forming the tensor product of the input with an array of ones, use kron. For example, to stack the row vector A = 1:3 four times vertically, you can use B = kron(A,ones(4,1)).
• To create block arrays and perform a binary operation in a single pass, use bsxfun. In some cases, bsxfun provides a simpler and more memory efficient solution. For example, to add the vectors A = 1:5 and B = (1:10)' to produce a 10-by-5 array, use bsxfun(@plus,A,B) instead of repmat(A,10,1) + repmat(B,1,5).
• When A is a scalar of a certain type, you can use other functions to get the same result as repmat.

  repmat Syntax	Equivalent Alternative
  repmat(NaN,m,n)	NaN(m,n)
  repmat(single(inf),m,n)	inf(m,n,'single')
  repmat(int8(0),m,n)	zeros(m,n,'int8')
  repmat(uint32(1),m,n)	ones(m,n,'uint32')
  repmat(eps,m,n)	eps(ones(m,n))

Extended Capabilities

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This function supports tall arrays with the limitations:

• The replication factor in the first dimension must be 1. For example, repmat(TA,1,n,p,...).

For more information, see Tall Arrays.

Usage notes and limitations:

• Size arguments must have a fixed size.
• For sparse matrices, the repmat function does not support trailing ones as inputs after the first two dimensions.

Usage notes and limitations:

• Size arguments must have a fixed size.
• For sparse matrices, the repmat function does not support trailing ones as inputs after the first two dimensions.

The repmat 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 before R2006a

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Starting in R2019b, some syntaxes involving nonscalar or empty repetition arguments will produce an error. The following table describes how to update these syntaxes.