Polars: how to add a column in front? [duplicate]

Question

What would be the most idiomatic (and efficient) way to add a column in front of a polars data frame? Same thing like .with_columns but add it at index 0?

Answer 1

You can select in the order you want your new DataFrame.

df = pl.DataFrame({
    "a": [1, 2, 3],
    "b": [True, None, False]
})

df.select(
    pl.lit("foo").alias("z"),
    pl.all()
)

shape: (3, 3)
┌─────┬─────┬───────┐
│ z   ┆ a   ┆ b     │
│ --- ┆ --- ┆ ---   │
│ str ┆ i64 ┆ bool  │
╞═════╪═════╪═══════╡
│ foo ┆ 1   ┆ true  │
│ foo ┆ 2   ┆ null  │
│ foo ┆ 3   ┆ false │
└─────┴─────┴───────┘