CODEWITHSUNDEEP
matlabmatrix
dustynrobots
dustynrobots

Reputation: 311

Matlab overwrite random columns in matrix with zeros?

I'm using the code below to replace random-looking columns in a matrix with zeros (in reality they're not random, but correspond to degrees of freedom of human movement). The code works, but I feel like there has to be a more efficient way to do this. The matrix has 128 columns and I'm not done yet!

subject(subNum).trial(trialNum).Qsagittal = subject(subNum).trial(trialNum).Q;
for column = 1:9
    switch column
        case 2
            subject(subNum).trial(trialNum).Qsagittal(:,column) = zeros(m,1);
        case 3
            subject(subNum).trial(trialNum).Qsagittal(:,column) = zeros(m,1);
        case 5
            subject(subNum).trial(trialNum).Qsagittal(:,column) = zeros(m,1);
        case 6
            subject(subNum).trial(trialNum).Qsagittal(:,column) = zeros(m,1);
        case 8
            subject(subNum).trial(trialNum).Qsagittal(:,column) = zeros(m,1);
        case 9
            subject(subNum).trial(trialNum).Qsagittal(:,column) = zeros(m,1);
   end
end

Upvotes: 0

Views: 274

Answers (1)

Dennis Jaheruddin
Dennis Jaheruddin

Reputation: 21563

As @jucestain suggested you don't need to update the columns 1 by one. Matlab allows you to enter a vector as indexing argument, so suppose you have:

idx = [2,3,5,6,8,9];

You can directly assign zero to all columns:

subject(subNum).trial(trialNum).Qsagittal(:,idx) = 0;

Just a guess, but it seems like you want each second and third number to be in idx. You can achieve this easily like so:

idx = 1:9; 
idx(1:3:9) = [];

For future reference, if someone actually wants to assign 6 out of 9 random columns to zero, it can be achieved by using this index:

idx = randperm(9,6)

Upvotes: 1

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