polars.Expr.list.len

Expr.list.len() → Expr

Return the number of elements in each list.

Null values are treated like regular elements in this context.

Returns:

Expr

Expression of data type UInt32.

Examples

>>> df = pl.DataFrame({"a": [[1, 2, None], [5]]})
>>> df.with_columns(len=pl.col("a").list.len())
shape: (2, 2)
┌──────────────┬─────┐
│ a            ┆ len │
│ ---          ┆ --- │
│ list[i64]    ┆ u32 │
╞══════════════╪═════╡
│ [1, 2, null] ┆ 3   │
│ [5]          ┆ 1   │
└──────────────┴─────┘