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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.

Azzi Abdelmalek on 17 Nov 2012

Why did you need to do it with if condition?

Bob Choy on 17 Nov 2012

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

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Answer by Matt Fig on 17 Nov 2012
Edited by Matt Fig on 17 Nov 2012

The number of zeros in the matrix A is:

```sum(~A(:))
```

So we can make this a function:

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

Now test it:

```x = [1 2 3;0 0 0;3 0 9]
f(x)
```

Bob Choy on 18 Nov 2012

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
end
M = 1 0 1 1
1 1 1 0
```

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

Matt Fig on 18 Nov 2012
```M = [1 0 1 1;1 1 1 0]
fid = fopen('mytext.txt','wt')
fprintf(fid,'%i ',find(sum(~M) >= 1))
fclose(fid)
```
Bob Choy on 18 Nov 2012

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

Answer by Andrei Bobrov on 17 Nov 2012

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

```numel(M) - nnz(M)