# Zero out values ​​from a specific row in a matrix

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Lev Mihailov am 24 Feb. 2022
Kommentiert: Jan am 24 Feb. 2022
I create a matrix, I need to reset all values ​​​​above or below a certain line
c = randi([50 90],1,900); % rows in the matrix before or after which you need to reset everything
x = rand(100,900);
I would appreciate any help
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Jan am 24 Feb. 2022
Does "reset" means, to set the value to 0? A small example with inputs and output would clarify this.

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### Akzeptierte Antwort

DGM am 24 Feb. 2022
Depends if you want before or after. Since there's no specified mechanism to determine which, I'm assuming they're separate cases.
% a smaller array
sz = [10 10];
c = randi(round([0.5 0.9]*sz(1)),1,sz(2))
c = 1×10
5 5 8 8 7 6 5 7 7 7
x = rand(sz);
% above
xa = zeros(sz);
for col = 1:sz(2)
xa(c(col):end,col) = x(c(col):end,col);
end
xa
xa = 10×10
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.6705 0.3275 0 0 0 0 0.8203 0 0 0 0.3977 0.2444 0 0 0 0.2563 0.6388 0 0 0 0.3504 0.4670 0 0 0.8608 0.6775 0.7311 0.6058 0.9829 0.5098 0.2348 0.4727 0.5051 0.7958 0.2300 0.5589 0.2007 0.7440 0.6406 0.1086 0.3023 0.2689 0.6540 0.5244 0.9616 0.0880 0.9428 0.1761 0.6237 0.5623 0.7242 0.2876 0.3713 0.6931 0.6045 0.1354 0.0207 0.3005 0.6675 0.9878
% below
xb = zeros(sz);
for col = 1:sz(2)
xb(1:c(col),col) = x(1:c(col),col);
end
xb
xb = 10×10
0.2351 0.8935 0.6577 0.1085 0.7050 0.7653 0.5715 0.1200 0.3469 0.8277 0.8900 0.0832 0.3699 0.4257 0.3712 0.8449 0.8821 0.3460 0.0425 0.6749 0.7048 0.9170 0.8989 0.5342 0.1087 0.4904 0.3728 0.1454 0.6048 0.0438 0.9782 0.3588 0.9342 0.3823 0.5303 0.7890 0.3342 0.0637 0.2030 0.5178 0.6705 0.3275 0.4531 0.0285 0.0355 0.8376 0.8203 0.1705 0.6936 0.4366 0 0 0.6351 0.0355 0.8810 0.2563 0 0.7491 0.8071 0.5694 0 0 0.1182 0.9483 0.8608 0 0 0.6058 0.9829 0.5098 0 0 0.5051 0.7958 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
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