METAL CustomVariables are user specified columns whose contents are tracked across multiple files. New variables are created with the CUSTOMVARIABLE command.
For example, the command:
Creates a custom variable called MENDEL_ERRORS. This variable must next be linked to specific columns in each input file with the LABEL command. For example:
LABEL MENDEL_ERRORS AS bad_transmissions PROCESS input_file1.txt LABEL MENDEL_ERRORS AS non_mendelian_events PROCESS input_file2.txt
In the example above, the column "bad_transmissions" in "input_file1.txt" and "non_mendelian_events" in "input_file2.txt" would be linked to the MENDEL_ERRORS column. Metal would report the sum of these two columns in each row of output.