CODEWITHSUNDEEP
arraysmatlab
rk_x23
rk_x23

Reputation: 45

Change one value of column based on value of another column in Matlab

I have two arrays in matlab (small part shown below):

    A     B
   2     3
   0,1   3,6
   0,1   3,6
   0,1   3,6
   0,1   3,2
   0     3,2
   0     3,2
   0     3,2
   0     2,4
   0     4,3
   0,1   4,3
   0,1   4,3
   0,1   4,3
   0,1   4,3
   0,1   4,3

What I want to do: If value in column A is zero, value in column B should be changed to zero or NaN.

I would appreciate any help regarding this! I am new to matlab and I am not sure if a 'for - end' loop can/should be used?

Thanks! :)

Upvotes: 0

Views: 208

Answers (1)

Eitan T
Eitan T

Reputation: 32930

You can use logical indexing:

B(A == 0) = 0;

The expression A == 0 returns a logical array (of booleans), containing "1"s at the positions that correspond to the zero elements in A. Feeding this boolean array into B, selects only the elements from B at the locations of the "1"s. The zero assignment is self-explanatory.

However, when A contains decimal values, Rody correctly pointed out that the comparison operation might be inaccurate and return false results. Therefore you should set a tolerance (e.g a multiple of eps), like so:

tol = eps;           %// Tolerance
B(abs(A) < tol) = 0;

If you don't care for floating point inaccuracy, and A niether contains NaN values nor complex numbers, you can use the following shortened syntax:

B(~A) = 0;

Upvotes: 4

Related Questions