Tests whether the first column of a data frame contains either
non-numeric values (default) or any of the potential_keywords
supplied.
is_key_column_present(data_table, potential_keywords = NULL)
A logical scalar: TRUE
if the key column is valid, otherwise throws
an error with a descriptive message.
A data frame with a key column in its first position.
Optional character vector of keywords expected in
the key column. Defaults to NULL
, in which case the function only asserts
that the first column is not numeric.