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Table.auto_cast

auto_castcolumnsshrink_typeserror_on_missing_columnson_problems

Group: Conversions
Aliases: auto_value_types

Documentation​

Automatically detect the appropriate data type and size for specified columns and change them, based on the contents. This is most useful for Mixed types to narrow down the type if all values could fit into one type.

Returns - A new table with the specified columns converted to the most appropriate type.

Arguments​

  • columns: The selection of columns to convert. Defaults to all columns.
  • shrink_types: If set True, smaller types will be chosen if possible, according to the rules below. Defaults to False. For example, from a 64-bit integer to a 32-bit integer if all fit.
  • error_on_missing_columns: Specifies if a missing input column should result in an error regardless of the on_problems settings. Defaults to True.
  • on_problems: Specifies how to handle problems if they occur, reporting them as warnings by default.

Remarks​

Auto Type Selection Rules​

  • If a Mixed column can be assigned a single type, like Char or Integer, that will be used.
  • Text columns are not parsed. To do that, use the parse method.
  • If a Float column contains only integers, it will be converted to an Integer column.
  • If a Decimal column contains only integers that could fit in a 64-bit integer storage, it will be converted to an Integer column.
  • If shrink_types is False (default), no other transformations are applied.
  • However, if shrink_types is set to True, then:
    • Integer columns will be assigned the smallest size that can fit all values (down to 16-bit integers; converting to the Byte type has to be done manually through cast).
    • If all elements in a text column have the same length, the type will become fixed length.
    • Otherwise, if a text column is variable length, but all text elements are no longer than 255 characters, the column will get a max length of 255. Otherwise, the column size limit will stay unchanged.