Check if Selected Columns in a Data Frame Contain Missing Values
has_no_missing_values(x, names)A list with two elements: 1) rqmt_ok which is TRUE if
the requirement is fulfilled and FALSE otherwise; 2)
err_message, the body of an error message to be used by the calling
function (mentions all problematic elements)
a data.frame
character vector containg the names of the columns in
x to be checked