polars.LazyFrame.unnest

LazyFrame.unnest(
    columns: ColumnNameOrSelector | Collection[ColumnNameOrSelector] | None = None,
    *more_columns: ColumnNameOrSelector,
    separator: str | None = None,
) → LazyFrame

Decompose struct columns into separate columns for each of their fields.

The new columns will be inserted into the DataFrame at the location of the struct column.

If no columns are provided, all struct columns are unnested.

engine:In MemoryStreamingDistributed

Parameters:

columns

Name of the struct column(s) that should be unnested.

*more_columns

Additional columns to unnest, specified as positional arguments.

separator

Rename output column names as combination of the struct column name, name separator and field name.

Examples

>>> df = pl.LazyFrame(
...     {
...         "before": ["foo", "bar"],
...         "t_a": [1, 2],
...         "t_b": ["a", "b"],
...         "t_c": [True, None],
...         "t_d": [[1, 2], [3]],
...         "after": ["baz", "womp"],
...     }
... ).select("before", pl.struct(pl.col("^t_.$")).alias("t_struct"), "after")
>>> df.collect()
shape: (2, 3)
┌────────┬─────────────────────┬───────┐
│ before ┆ t_struct            ┆ after │
│ ---    ┆ ---                 ┆ ---   │
│ str    ┆ struct[4]           ┆ str   │
╞════════╪═════════════════════╪═══════╡
│ foo    ┆ {1,"a",true,[1, 2]} ┆ baz   │
│ bar    ┆ {2,"b",null,[3]}    ┆ womp  │
└────────┴─────────────────────┴───────┘
>>> df.unnest("t_struct").collect()
shape: (2, 6)
┌────────┬─────┬─────┬──────┬───────────┬───────┐
│ before ┆ t_a ┆ t_b ┆ t_c  ┆ t_d       ┆ after │
│ ---    ┆ --- ┆ --- ┆ ---  ┆ ---       ┆ ---   │
│ str    ┆ i64 ┆ str ┆ bool ┆ list[i64] ┆ str   │
╞════════╪═════╪═════╪══════╪═══════════╪═══════╡
│ foo    ┆ 1   ┆ a   ┆ true ┆ [1, 2]    ┆ baz   │
│ bar    ┆ 2   ┆ b   ┆ null ┆ [3]       ┆ womp  │
└────────┴─────┴─────┴──────┴───────────┴───────┘

Unnest all struct columns by calling without arguments:

>>> df.unnest().collect()
shape: (2, 6)
┌────────┬─────┬─────┬──────┬───────────┬───────┐
│ before ┆ t_a ┆ t_b ┆ t_c  ┆ t_d       ┆ after │
│ ---    ┆ --- ┆ --- ┆ ---  ┆ ---       ┆ ---   │
│ str    ┆ i64 ┆ str ┆ bool ┆ list[i64] ┆ str   │
╞════════╪═════╪═════╪══════╪═══════════╪═══════╡
│ foo    ┆ 1   ┆ a   ┆ true ┆ [1, 2]    ┆ baz   │
│ bar    ┆ 2   ┆ b   ┆ null ┆ [3]       ┆ womp  │
└────────┴─────┴─────┴──────┴───────────┴───────┘

>>> df = pl.LazyFrame(
...     {
...         "before": ["foo", "bar"],
...         "t_a": [1, 2],
...         "t_b": ["a", "b"],
...         "t_c": [True, None],
...         "t_d": [[1, 2], [3]],
...         "after": ["baz", "womp"],
...     }
... ).select(
...     "before",
...     pl.struct(pl.col("^t_.$").name.map(lambda t: t[2:])).alias("t"),
...     "after",
... )
>>> df.unnest("t", separator="::").collect()
shape: (2, 6)
┌────────┬──────┬──────┬──────┬───────────┬───────┐
│ before ┆ t::a ┆ t::b ┆ t::c ┆ t::d      ┆ after │
│ ---    ┆ ---  ┆ ---  ┆ ---  ┆ ---       ┆ ---   │
│ str    ┆ i64  ┆ str  ┆ bool ┆ list[i64] ┆ str   │
╞════════╪══════╪══════╪══════╪═══════════╪═══════╡
│ foo    ┆ 1    ┆ a    ┆ true ┆ [1, 2]    ┆ baz   │
│ bar    ┆ 2    ┆ b    ┆ null ┆ [3]       ┆ womp  │
└────────┴──────┴──────┴──────┴───────────┴───────┘