WHERE(x) produces a variate listing the units of
x that are logically true, i.e. non-zero (synonym
WHICH). If all the units are false, it produces a variate of length one, containing a missing value. If
x is restricted or qualified (by
WHERE looks only in the defined subset of units for true values. However, the unit numbers in the result give their positions in the full vector
x, not the subset.
Updated on December 4, 2017