Subset$byRowNames: Extract subset of columns from a data frame or a list of data frames
Description
Extract subset of columns from a data frame or a list of data frames.
This function outputs a data frame which set of rows is a product of merging according to mergeOp
of the imput data frame row set with a given set of names (subset) ordred either by the original row set
or by a a subset parameter according to orderBySubset flag. In case the merging operation produces the rows
which are not in an original data frame, the new rows are filled with value from na.value parameter.