Take a character, logical, or integer vector and return the appropriate names
of the crdf to subset. Disallow logicals (in the case of [[
subsetting, to
conform with data.frame
methods)
grabColNames(x, j, allow_logical = TRUE)
crdf to grab columns from
character, logical, or integer vector specifying the columns to grab
logical should logical subsetting be allowed? (default: TRUE)
character names of the columns of the crdf to select