Get row metadata
Get linked row metadata from a matrix or data frame
Matrix or data frame
IF set to NULL, no handler is called.
When called with an M-row dataset that has an attribute called "Row_Metadata" set to c(table = table_name, key = key_name), where table_name is the name of an existing row metadata table and key_name is the name of the primary ID key, this function will return the M x N "ProtInfo" table, where the first column is identical to the rownames of the dataset, and the other columns are the other row metadata fields.