DataFrameStatFunctions.
cov
Calculate the sample covariance for the given columns, specified by their names, as a double value. DataFrame.cov() and DataFrameStatFunctions.cov() are aliases.
DataFrame.cov()
DataFrameStatFunctions.cov()
col1 – The name of the first column
col2 – The name of the second column
New in version 1.4.