mask

mask(X, Y)

X is a scalar/vector/matrix.

Y is a conditional expression that generates true or false.

Apply Y on each element of X. If the result is false, keep the element; if the result is true, change it to NULL. The result is of the same length as X.

x=1..10
mask(x, x>6);
// output
[1,2,3,4,5,6,,,,]

m=matrix(1 2 3, 4 5 6, 7 8 9);
m;

mask(m, m<6);