polars.first#

polars.first(*columns: str) → Expr[source]#

Get the first column or value.

This function has different behavior depending on the presence of columns values. If none given (the default), returns an expression that takes the first column of the context; otherwise, takes the first value of the given column(s).

Parameters:

*columns: One or more column names.

Examples

>>> df = pl.DataFrame(
...     {
...         "a": [1, 8, 3],
...         "b": [4, 5, 2],
...         "c": ["foo", "bar", "baz"],
...     }
... )

Return the first column:

>>> df.select(pl.first())
shape: (3, 1)
┌─────┐
│ a   │
│ --- │
│ i64 │
╞═════╡
│ 1   │
│ 8   │
│ 3   │
└─────┘

Return the first value for the given column(s):

>>> df.select(pl.first("b"))
shape: (1, 1)
┌─────┐
│ b   │
│ --- │
│ i64 │
╞═════╡
│ 4   │
└─────┘
>>> df.select(pl.first("a", "c"))
shape: (1, 2)
┌─────┬─────┐
│ a   ┆ c   │
│ --- ┆ --- │
│ i64 ┆ str │
╞═════╪═════╡
│ 1   ┆ foo │
└─────┴─────┘