Calculates the number of non-missing observations in a data set (X and Y).
X is the input (explanatory) variables of the data set (two dimensional array of cells, where each column corresponds to a variable).
Mask is the boolean array to choose the input variables in the set. If missing, all variables in X are included.
Y is the dependent variable data set (one dimensional array of cells).
- In case of a missing mask input, all variables in X are considered.
- In case the number of the size of the mask array is smaller than the number of variables in X, the array is appeded with ones to match X.
- In case the number of the size of the mask array is greater than the number of variables in X, the excess elements are dropped/ignored.