The SKEWNESS function computes the statistical skewness of an n -element vector. If the variance of the vector is zero, the skewness is not defined, and SKEWNESS returns !VALUES.F_NAN as the result. SKEWNESS calls the IDL function MOMENT.
Set this keyword to cause the routine to check for occurrences of the IEEE floating-point value NaN in the input data. Elements with the value NaN are treated as missing data. (See Special Floating-Point Values for more information on IEEE floating-point values.)