polars.col¶

polars.col(name: Union[str, List[str], List[Type[polars.datatypes.DataType]], polars.internals.series.Series, Type[polars.datatypes.DataType]]) → polars.internals.expr.Expr¶

A column in a DataFrame. Can be used to select:

a single column by name
all columns by using a wildcard “*”
column by regular expression if the regex starts with ^ and ends with $

Parameters

name: A string that holds the name of the column

Examples

>>> df = pl.DataFrame(
...     {
...         "ham": [1, 2, 3],
...         "hamburger": [11, 22, 33],
...         "foo": [3, 2, 1],
...     }
... )
>>> df.select(pl.col("foo"))
shape: (3, 1)
┌─────┐
│ foo │
│ --- │
│ i64 │
╞═════╡
│ 3   │
├╌╌╌╌╌┤
│ 2   │
├╌╌╌╌╌┤
│ 1   │
└─────┘
>>> df.select(pl.col("*"))
shape: (3, 3)
┌─────┬───────────┬─────┐
│ ham ┆ hamburger ┆ foo │
│ --- ┆ ---       ┆ --- │
│ i64 ┆ i64       ┆ i64 │
╞═════╪═══════════╪═════╡
│ 1   ┆ 11        ┆ 3   │
├╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌┤
│ 2   ┆ 22        ┆ 2   │
├╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌┤
│ 3   ┆ 33        ┆ 1   │
└─────┴───────────┴─────┘
>>> df.select(pl.col("^ham.*$"))
shape: (3, 2)
┌─────┬───────────┐
│ ham ┆ hamburger │
│ --- ┆ ---       │
│ i64 ┆ i64       │
╞═════╪═══════════╡
│ 1   ┆ 11        │
├╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌┤
│ 2   ┆ 22        │
├╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌┤
│ 3   ┆ 33        │
└─────┴───────────┘
>>> df.select(pl.col("*").exclude("ham"))
shape: (3, 2)
┌───────────┬─────┐
│ hamburger ┆ foo │
│ ---       ┆ --- │
│ i64       ┆ i64 │
╞═══════════╪═════╡
│ 11        ┆ 3   │
├╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌┤
│ 22        ┆ 2   │
├╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌┤
│ 33        ┆ 1   │
└───────────┴─────┘
>>> df.select(pl.col(["hamburger", "foo"]))
shape: (3, 2)
┌───────────┬─────┐
│ hamburger ┆ foo │
│ ---       ┆ --- │
│ i64       ┆ i64 │
╞═══════════╪═════╡
│ 11        ┆ 3   │
├╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌┤
│ 22        ┆ 2   │
├╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌┤
│ 33        ┆ 1   │
└───────────┴─────┘

polars.select polars.count