Return a column's name
Character. Specifies the column to choose: "nt" chooses the CDR3 nucleotide column, "aa" chooses the CDR3 amino acid column, "v" chooses the V gene segment column, "j" chooses the J gene segment column.
A string that specifies the column(s) to be processed. Select one of the following strings, separated by the plus sign: "nt" for nucleotide sequences, "aa" for amino acid sequences, "v" for V gene segments, "j" for J gene segments.
A column's name.