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Number of zeros in a matrix

Asked by Bob Choy on 17 Nov 2012

I need to create a function where I have a matrix and the function returns the number of zeros in that matrix. I need to do this using the if condition.

Then write in a .txt file which columns had more than 12 zeros.

Can someone help me out with this?

Thank you very much.


Why did you need to do it with if condition?

Because thats what I usually work with but if thats impossible nevermind it.

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3 Answers

Answer by Loginatorist on 17 Nov 2012
Edited by Loginatorist on 17 Nov 2012
 Accepted Answer

The number of zeros in the matrix A is:


So we can make this a function:

f = @(x) sum(~x(:));

Now test it:

x = [1 2 3;0 0 0;3 0 9]


I want to write in a .txt file numbers of the columns that have more than 12 zeros. E.g. say I wanted the columns with atleast one zero. (Ignore the "if true" nonsense]

if true
  % code
M = 1 0 1 1
    1 1 1 0

I want the function to save a .txt file with the numbers 2 and 4.

M = [1 0 1 1;1 1 1 0]
fid = fopen('mytext.txt','wt')
fprintf(fid,'%i ',find(sum(~M) >= 1))

Thank you so much! Keep up the good work, cheers!

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Answer by Andrei Bobrov
on 17 Nov 2012

a - your matrix

number_columns = find(sum(~a) > 12);


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Answer by Walter Roberson
on 18 Nov 2012

numel(M) - nnz(M)


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