For each row, find the standard deviation among the columns from cols
skipping missing values. If a row contains only the missing values,
this function will produce a missing value too.
Parameters
f-expression consisting of one column that has the same number of rows
as in cols. The column stype is float32 when all the cols
are float32, and float64 in all the other cases.
The exception is raised when cols has non-numeric columns.