polars.LazyFrame.with_row_index#

LazyFrame.with_row_index(name: str = 'index', offset: int = 0) → Self[source]#

Add a row index as the first column in the LazyFrame.

Parameters:

name: Name of the index column.
offset: Start the index at this offset. Cannot be negative.

Warning

Using this function can have a negative effect on query performance. This may, for instance, block predicate pushdown optimization.

Notes

The resulting column does not have any special properties. It is a regular column of type UInt32 (or UInt64 in polars-u64-idx).

Examples

>>> lf = pl.LazyFrame(
...     {
...         "a": [1, 3, 5],
...         "b": [2, 4, 6],
...     }
... )
>>> lf.with_row_index().collect()
shape: (3, 3)
┌───────┬─────┬─────┐
│ index ┆ a   ┆ b   │
│ ---   ┆ --- ┆ --- │
│ u32   ┆ i64 ┆ i64 │
╞═══════╪═════╪═════╡
│ 0     ┆ 1   ┆ 2   │
│ 1     ┆ 3   ┆ 4   │
│ 2     ┆ 5   ┆ 6   │
└───────┴─────┴─────┘
>>> lf.with_row_index("id", offset=1000).collect()
shape: (3, 3)
┌──────┬─────┬─────┐
│ id   ┆ a   ┆ b   │
│ ---  ┆ --- ┆ --- │
│ u32  ┆ i64 ┆ i64 │
╞══════╪═════╪═════╡
│ 1000 ┆ 1   ┆ 2   │
│ 1001 ┆ 3   ┆ 4   │
│ 1002 ┆ 5   ┆ 6   │
└──────┴─────┴─────┘

An index column can also be created using the expressions int_range() and len().

>>> lf.select(
...     pl.int_range(pl.len(), dtype=pl.UInt32).alias("index"),
...     pl.all(),
... ).collect()
shape: (3, 3)
┌───────┬─────┬─────┐
│ index ┆ a   ┆ b   │
│ ---   ┆ --- ┆ --- │
│ u32   ┆ i64 ┆ i64 │
╞═══════╪═════╪═════╡
│ 0     ┆ 1   ┆ 2   │
│ 1     ┆ 3   ┆ 4   │
│ 2     ┆ 5   ┆ 6   │
└───────┴─────┴─────┘