IQR calculates the range of Y
Missing values (encoded as NaN) are ignored.
Q = range(Y)
Q = range(Y,DIM)
returns the range along dimension DIM of sample array Y.
Q = range(HIS)
returns the IQR from the histogram HIS.
HIS must be a HISTOGRAM struct as defined in HISTO2 or HISTO3.
see also: IQR, MAD, HISTO2, HISTO3, PERCENTILE, QUANTILE