Zero out values from a specific row in a matrix

Question

Lev Mihailov 2022-2-24

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https://ww2.mathworks.cn/matlabcentral/answers/1657390-zero-out-values-from-a-specific-row-in-a-matrix

评论： Jan 2022-2-24

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 2022-2-24

Does "reset" means, to set the value to 0? A small example with inputs and output would clarify this.

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Answer 1

DGM 2022-2-24

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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