Using a column vector of indices to replace values in a matrix

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Teddy Fisher 2019-12-13

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评论： sruizpp 2020-11-18

Hello,

I have a column vector, C, (55x1 double) which are the indices of my values of interest in Matrix, M which is 370x29 double.

I want to replace all the values in M that are not these values of interest with 0.

I am trying to use C to index into M and replace ~C with 0.

However when I try

M(~C)=0

all it does is change all the values in M to just different values and I'm not sure why.

When I try to create a new Matrix

N=M(~C==0) it returns a columnn vector with just the first 55 values in the first column of M.

Does anyone know how I can replace all the elements in M that are not listed in C with 0? I want my output to be another 370x29 double matrix.

Thanks!

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Teddy Fisher 2019-12-13

I had another Matrix, R, that was 0s and 1s, also 370x29 double

I used

C=find(R) to get the indexes of the 1s in R (which correspond to the values I want in M)

So the values in C are numbers (between 1-10730), not [row,column] format

Is there any way I can use C to index into M ?

Fangjun Jiang 2019-12-13

with this comments, the answer below should provide one solution.

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Answer 1

Fangjun Jiang 2019-12-13

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https://ww2.mathworks.cn/matlabcentral/answers/496528-using-a-column-vector-of-indices-to-replace-values-in-a-matrix#answer_406289

编辑：Fangjun Jiang 2019-12-13

在 MATLAB Online 中打开

C=[1,2,3]';
M=magic(5);
index=setdiff(1:numel(M),C);
M(index)=0

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Teddy Fisher 2019-12-13

Thank you so much!! I can't tell you how much this helped

sruizpp 2020-11-18

c00L

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Answer 2

Guillaume 2019-12-13

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https://ww2.mathworks.cn/matlabcentral/answers/496528-using-a-column-vector-of-indices-to-replace-values-in-a-matrix#answer_406302

编辑：Guillaume 2019-12-13

在 MATLAB Online 中打开

Well, now you have explained how you got C, a much simpler method than the accepted one is not to create C and use:

M(~R) = 0; %that's all that is needed!

As usual in matlab, find is completely unnecessary and what you were trying to do initially would have worked had you kept your original logical vector.

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Fangjun Jiang 2019-12-13

indeed!

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