type_convert: Re-convert character columns in existing data frame.
Description
This is useful if you need to do some manual munging - you can read the
columns in as character, clean it up with (e.g.) regular expressions and
then let readr take another stab at parsing it.
Usage
type_convert(df, col_types = NULL)
Arguments
df
A data frame.
col_types
One of NULL, a list, a named list or a string.
If NULL, the column type will be imputed from the first 30 rows
on the input. This is convenient (and fast), but not robust. If the
imputation fails, you'll need to supply the