not_constant

checks.not_constant(data, columns=None, group_by=None)

Check if a DataFrame has constant columns.

Parameters

data: PolarsLazyOrDataFrame

The input DataFrame to check for null values.

columns: Optional[PolarsColumnType] = None

Columns to consider for null value check. By default, all columns are checked.

group_by: Optional[PolarsOverClauseInput] = None

When specified perform the check per group instead of the whole column, by default None

Returns

Type	Description
PolarsLazyOrDataFrame	The original polars DataFrame or LazyFrame when the check passes

Examples

>>> import polars as pl
>>> import pelage as plg
>>> df = pl.DataFrame({"a": [1, 2]})
>>> df.pipe(plg.not_constant, "a")
shape: (2, 1)
┌─────┐
│ a   │
│ --- │
│ i64 │
╞═════╡
│ 1   │
│ 2   │
└─────┘
>>> df = pl.DataFrame({"b": [1, 1]})
>>> df.pipe(plg.not_constant)
Traceback (most recent call last):
...
pelage.checks.PolarsAssertError: Details
shape: (1, 2)
┌────────┬────────────┐
│ column ┆ n_distinct │
│ ---    ┆ ---        │
│ str    ┆ u32        │
╞════════╪════════════╡
│ b      ┆ 1          │
└────────┴────────────┘
Error with the DataFrame passed to the check function:
--> Some columns are constant

The folloing example details how to perform this checks for groups:

>>> import polars as pl
>>> import pelage as plg
>>> df = pl.DataFrame(
...     {
...         "a": [1, 2, 1, 1],
...         "b": ["A", "A", "B", "B"],
...     }
... )
>>> df.pipe(plg.not_constant, "a")
shape: (4, 2)
┌─────┬─────┐
│ a   ┆ b   │
│ --- ┆ --- │
│ i64 ┆ str │
╞═════╪═════╡
│ 1   ┆ A   │
│ 2   ┆ A   │
│ 1   ┆ B   │
│ 1   ┆ B   │
└─────┴─────┘
>>> df.pipe(plg.not_constant, "a", group_by="b")
Traceback (most recent call last):
...
pelage.checks.PolarsAssertError: Details
shape: (1, 3)
┌─────┬────────┬────────────┐
│ b   ┆ column ┆ n_distinct │
│ --- ┆ ---    ┆ ---        │
│ str ┆ str    ┆ u32        │
╞═════╪════════╪════════════╡
│ B   ┆ a      ┆ 1          │
└─────┴────────┴────────────┘
Error with the DataFrame passed to the check function:
--> Some columns are constant within a given group