named_vec_to_df: Convert a named vector returned from vapply to a dataframe
Description
When running a vapply function and each element returns a single value,
the return value is a named vector. This function can be used to convert
that return value into a data.frame. Similar to lol_to_df,
but because the output format from vapply is different depending on
whether a single value or multiple values are returned, a different function
needs to be used.