col_types_standardise(col_types, col_names, guessed_types)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 correct types yourself.
If a list, it must contain one "collector" for each column.
If you only want to read a subset of the columns, you can use a named list
(where the names give the column names). If a column is not mentioned by
name, it will not be included in the output.
Alternatively, you can use a compact string representation where each
character represents one column: c = character, d = double, i = integer,
l = logical and _ skips the column.