How to duplicate elements of a matrix without using the repmat function

问题

Given the matrix I = [1,2;3,4], I would like to duplicate the elements to create a matrix I2 such that:

I2 = [1 1 1 2 2 2
      1 1 1 2 2 2
      1 1 1 2 2 2
      3 3 3 4 4 4 
      3 3 3 4 4 4
      3 3 3 4 4 4]

Other than using repmat, what other methods or functions are available?

回答1:

Use kron:

>> N = 3 %// Number of times to replicate a number in each dimension
>> I = [1,2;3,4];
>> kron(I, ones(N))

ans =

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

This probably deserves some explanation in case you're not aware of what kron does. kron stands for the Kronecker Tensor Product. kron between two matrices A of size m x n and B of size p x q creates an output matrix of size mp x nq such that:

Therefore, for each coefficient in A, we take this value, multiply it with every value in the matrix B and we position these matrices in the same order as we see in A. As such, if we let A = I, and B be the 3 x 3 matrix full of ones, you thus get the above result.

回答2:

Using indexing:

I = [1, 2; 3, 4];                                           %// original matrix
n = 3;                                                      %// repetition factor
I2 = I(ceil(1/n:1/n:size(I,1)), ceil(1/n:1/n:size(I,2)));   %// result

回答3:

One-liner with bsxfun -

R = 3; %// Number of replications
I2 = reshape(bsxfun(@plus,permute(I,[3 1 4 2]),zeros(R,1,R)),R*size(I,1),[])

Sample run -

I =
     3     2     5
     9     8     9
I2 =
     3     3     3     2     2     2     5     5     5
     3     3     3     2     2     2     5     5     5
     3     3     3     2     2     2     5     5     5
     9     9     9     8     8     8     9     9     9
     9     9     9     8     8     8     9     9     9
     9     9     9     8     8     8     9     9     9

来源：https://stackoverflow.com/questions/28847890/how-to-duplicate-elements-of-a-matrix-without-using-the-repmat-function

标签

matlab

matrix