month_delta return incorrect value if passed a date object

[pounde]

I am attempting to replicate the functionality of relativedelta. The month_delta meets my current purposes but it return incorrect values if passed a date object.

This provided incorrect results. I would expect correct values or a ValueError

    df_ = df.filter(pl.col("date") <= end_date).with_columns(
        yr_for_calc=xdt.month_delta(pl.col("date"), end_date) / 12
    )

The following was my workaround:

    df_ = (
        df.filter(pl.col("date") <= end_date)
        .with_columns(end_date=end_date)
        .with_columns(
            yr_for_calc=xdt.month_delta(pl.col("date"), pl.col("end_date")) / 12
        )
    ).drop("end_date")

[MarcoGorelli]

thanks @pounde for the report

could you include a reproducible example please?

If I run

# ruff: noqa
from datetime import date, datetime
import polars as pl
import polars_xdt as xdt
df = pl.DataFrame(
    {
        "start_date": [
            date(2024, 3, 1),
            date(2024, 3, 31),
            date(2022, 2, 28),
            date(2023, 1, 31),
            date(2019, 12, 31),
        ],
        "end_date": [
            date(2023, 2, 28),
            date(2023, 2, 28),
            date(2023, 2, 28),
            date(2023, 1, 31),
            date(2023, 1, 1),
        ],
    },
)
print(df.with_columns(
    xdt.month_delta("start_date", date(2023, 2, 28)).alias("month_delta")
))
print(df.with_columns(
    xdt.month_delta("start_date", datetime(2023, 2, 28)).alias("month_delta")
))

then I do indeed get an error

polars.exceptions.ComputeError: the plugin failed with message: polars_xdt.month_delta only works on Date type. Please cast to Date first.

[pounde]

Apologies for not doing that from the start. I can't seem to replicate my code, nor can I replicate the code you posted. It is also worth noting that the object passed in the original issue was a 'date' object, not 'datetime'. I have updated the title to reflect that.

While attempting to run the code you provided, I get:

[line 22](vscode-notebook-cell:?execution_count=36&line=22)InvalidOperationError: Series month_delta, length 1 doesn't match the DataFrame height of 5

If you want expression: col("start_date")./usr/local/lib/python3.10/site-packages/polars_xdt/_internal.abi3.so:month_delta([2023-02-28]) to be broadcasted, ensure it is a scalar (for instance by adding '.first()').

Not sure why I didn't get this before, nor why it can't be broadcast.

[MarcoGorelli]

While attempting to run the code you provided, I get:

are you sure you got that while running the code I posted? could you post the full traceback please?