polars.Expr.struct.field#

Expr.struct.field(name: str | list[str], *more_names: str) → Expr[source]#

Retrieve one or multiple Struct field(s) as a new Series.

Parameters:

name: Name of the struct field to retrieve.
*more_names: Additional struct field names.

Notes

The struct namespace has implemented __getitem__ so you can also access fields by index:

>>> df.select(pl.col("struct_col").struct[1])
shape: (2, 1)
┌─────┐
│ bbb │
│ --- │
│ str │
╞═════╡
│ ab  │
│ cd  │
└─────┘

Examples

>>> df = pl.DataFrame(
...     {
...         "aaa": [1, 2],
...         "bbb": ["ab", "cd"],
...         "ccc": [True, None],
...         "ddd": [[1, 2], [3]],
...     }
... ).select(pl.struct("aaa", "bbb", "ccc", "ddd").alias("struct_col"))
>>> df
shape: (2, 1)
┌──────────────────────┐
│ struct_col           │
│ ---                  │
│ struct[4]            │
╞══════════════════════╡
│ {1,"ab",true,[1, 2]} │
│ {2,"cd",null,[3]}    │
└──────────────────────┘

Retrieve struct field(s) as Series:

>>> df.select(pl.col("struct_col").struct.field("bbb"))
shape: (2, 1)
┌─────┐
│ bbb │
│ --- │
│ str │
╞═════╡
│ ab  │
│ cd  │
└─────┘

>>> df.select(
...     pl.col("struct_col").struct.field("bbb"),
...     pl.col("struct_col").struct.field("ddd"),
... )
shape: (2, 2)
┌─────┬───────────┐
│ bbb ┆ ddd       │
│ --- ┆ ---       │
│ str ┆ list[i64] │
╞═════╪═══════════╡
│ ab  ┆ [1, 2]    │
│ cd  ┆ [3]       │
└─────┴───────────┘

Use wildcard expansion:

>>> df.select(pl.col("struct_col").struct.field("*"))
shape: (2, 4)
┌─────┬─────┬──────┬───────────┐
│ aaa ┆ bbb ┆ ccc  ┆ ddd       │
│ --- ┆ --- ┆ ---  ┆ ---       │
│ i64 ┆ str ┆ bool ┆ list[i64] │
╞═════╪═════╪══════╪═══════════╡
│ 1   ┆ ab  ┆ true ┆ [1, 2]    │
│ 2   ┆ cd  ┆ null ┆ [3]       │
└─────┴─────┴──────┴───────────┘

Retrieve multiple fields by name:

>>> df.select(pl.col("struct_col").struct.field("aaa", "bbb"))
shape: (2, 2)
┌─────┬─────┐
│ aaa ┆ bbb │
│ --- ┆ --- │
│ i64 ┆ str │
╞═════╪═════╡
│ 1   ┆ ab  │
│ 2   ┆ cd  │
└─────┴─────┘

Retrieve multiple fields by regex expansion:

>>> df.select(pl.col("struct_col").struct.field("^a.*|b.*$"))
shape: (2, 2)
┌─────┬─────┐
│ aaa ┆ bbb │
│ --- ┆ --- │
│ i64 ┆ str │
╞═════╪═════╡
│ 1   ┆ ab  │
│ 2   ┆ cd  │
└─────┴─────┘