Copy specific array cells into another column of same array - MatLab

I have a cell array of dimension 20000x3

each column of cells came from a separate array. using the following I concatenated them into one

array4 = [array1,array2,array3];

for array4( ,3) i want to copy certain cells into array4( ,4) and array4( ,5) when an if statement is true

if abs((find(a==-1)-(find(a==)-1))) > 200
    array4(:,4) = find(a==-1);
    array4(:,5) = find(a==1);
end

my if loop above is not working... there are no error messages but there is nothing in the forth and fifth columns of array4

could somebody help me fix finding the indices within the if loop - I think this is the problem?

thanks for any help!