pub fn widths(reader: &Reader) -> Vec<(String, u64)>Expand description
How many bytes a value of each string column takes on average, by name.
Read off the column’s summary, which counts the bytes of every value that is not null, so this is exact as an average and says nothing about how the lengths spread. A column with no summary, or with nothing in it but nulls, is left out, and a column left out is priced as the header a string always has.