MATLAB Answers


set some values to zero in a matrix

Asked by Nikolaos Zafirakis on 13 Apr 2019
Latest activity Commented on by Nikolaos Zafirakis on 14 Apr 2019
Hello, I have a 6x20000 matrix. I would like make the 3 smalest values on each row equal to zero. For example if I have:
[ 1, 1, 1, 1.5, 1.5, 1.5 = [ 0, 0, 0, 1.5, 1.5, 1.5
1, 1.5, 1, 1, 1.5, 1.5 0, 1.5, 0, 0, 1.5, 1.5
1, 1.5, 1, 1, 1.5, 1.5] 0, 1.5, 0, 0, 1.5, 1.5]
Does anyone know how to do this?


What do you want to do if there are four or more copies of the same minimum value?
What do you want to do if there is a distinct minumum value, but then there is a tie for second or third place such that the total number of values no greater than the third smallest, is more than 3? Such as [1 1.5 1 1.5 1.5 1.5]: here the two 1's are smallest, but there is a tie of 1.5's for third.
Hello well I actually took the code supplied by madhan below. The matrix is coordinates x-y-z and -x -y -z. I split the matrix into 3 sections making x and -x one matrix y and -y another ...etc. Then I applied the code by madhan to the 2x20000 matrix and took the largest value from this. Then I combined the matrix back together and have one value for each plane.

Sign in to comment.

1 Answer

Answer by madhan ravi
on 14 Apr 2019
Edited by madhan ravi
on 14 Apr 2019

Note: Have the same doubt as sir Walter but see if the below answer does what you want.
[~,I]=mink(a,3,2); % requires 2017 b and later if prior sort each row and pick first three values in each row, a is your matrix
idx=sub2ind(size(a), repmat((1:size(a,1)).',1,size(I,2)) ,I);

  1 Comment

Thanks that was very helpful! (See above i solved the issue).

Sign in to comment.