CODEWITHSUNDEEP
arraysmatlab
Stewie Griffin
Stewie Griffin

Reputation: 14939

Change values in matrix without loops in Matlab

I have an array where I want to change the values in certain columns according to an "indexing-array".

Suppose I have an array A, where the values in column 1 and 2 are to be switched according to the matrix switch_mat, below.

A(:,[1 2]) =         
 1     2    
 2     6
 2     7
 6     7
 7    12
 7    13
12    13

switch_mat =
 1     1
 2     2
 6     3
 7     4
12     5
13     6

Is it possible to do this without loops, using some functions like this?

A(:,[1 2]) = renum(A(:,[1 2]),switch_mat)

The new A matrix will be:

A(:,[1 2]) = 
 1     2    
 2     3
 2     4 
 3     4
 4     5
 4     6
 5     6

Thanks!

EDIT: The switch in the A matrix will be:

1  -> 1
2  -> 2
6  -> 3
7  -> 4
12 -> 5
13 -> 6   % 13 becomes a 6, because they are in the same row of switch_mat

The dimension of switch_mat = length(unique(A))

Upvotes: 0

Views: 724

Answers (1)

Eitan T
Eitan T

Reputation: 32930

Here's a possible solution with arrayfun:

A = arrayfun(@(x)switch_mat(switch_mat(:, 1) == x, 2), A);

Alternatively, you can use ismember:

[tf, loc] = ismember(A, switch_mat(:, 1));
A(loc > 0) = switch_mat(loc(loc > 0), 2);

I believe the latter method should be faster.

Upvotes: 2

Related Questions