narwhals.Expr.list
len() -> ExprT
Return the number of elements in each list.
Null values count towards the total.
Returns:
Type | Description |
---|---|
ExprT
|
A new expression. |
Examples:
>>> import polars as pl
>>> import narwhals as nw
>>> df_native = pl.DataFrame({"a": [[1, 2], [3, 4, None], None, []]})
>>> df = nw.from_native(df_native)
>>> df.with_columns(a_len=nw.col("a").list.len())
┌────────────────────────┐
| Narwhals DataFrame |
|------------------------|
|shape: (4, 2) |
|┌──────────────┬───────┐|
|│ a ┆ a_len │|
|│ --- ┆ --- │|
|│ list[i64] ┆ u32 │|
|╞══════════════╪═══════╡|
|│ [1, 2] ┆ 2 │|
|│ [3, 4, null] ┆ 3 │|
|│ null ┆ null │|
|│ [] ┆ 0 │|
|└──────────────┴───────┘|
└────────────────────────┘