如何找到至少包含k个非零元素的列的索引？

Question

I have a matrix A as follows:

A =

     1     2     0     0     4
     0     0     0     1     3
     0     0     1     1     1

I would like to find the indecies of column A where each column has more than k-nonero elements. I used:

find(all(A~=0));

but it returns the index of the columns where there exist at least one non-zero element.

Answer 1

It might help you if you take it step by step.
First, find the number of nonzero elements in each column:

nNonZero = sum(A~=0)

Then find the columns that are more than k

find(nNonZero>k)

Answer 2

Instead of checking where all the values in a row are non-zero, rather count how many are and then apply your threshold:

k = 3
find(sum(A~=0,2)>=k)

returns:

ans =

   1
   3