Counting elements in a matrix that meet a certain condition

[Jane Evans]

I have converted the results from an estimation command to a matrix of size 100 x 1 (e.g. mat A= e(W_weights)). I am looking to count the number of elements in that column that are not equal to zero (and save that number in a local). Is there a way to do that?

[Clyde Schechter]

local wanted = 0
forvalues i = 1/100 {
    local wanted = `wanted' + (A[`i', 1] != 0)
}
display `wanted'

[Nick Cox]

If the number of observations is at least 100, you could do this

gen Amat = A[_n, 1] 
count if Amat != 0 in 1/100

There is also svmat -- but I could have typed out the above in the time that I had re-discovered the syntax of svmat, which I have not used much since Mata was introduced.

And now that Mata has been mentioned

mata : sum(st_matrix("A") :!= 0)

Zero-line solutions would be of interest too.