polars.LazyFrame.with_row_count#

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

Add a column at index 0 that counts the rows.

Parameters:

name: Name of the column to add.
offset: Start the row count at this offset.

Warning

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

Examples

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