set some values to zero in a matrix

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Nikolaos Zafirakis 2019-4-13

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评论： Nikolaos Zafirakis 2019-4-14

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?

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Walter Roberson 2019-4-14

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.

Nikolaos Zafirakis 2019-4-14

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.

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Answer 1

madhan ravi 2019-4-14

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https://ww2.mathworks.cn/matlabcentral/answers/456193-set-some-values-to-zero-in-a-matrix#answer_370512

编辑：madhan ravi 2019-4-14

在 MATLAB Online 中打开

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);
a(idx)=0