How to filter a polars dataframe by date?

Question

df.filter(pl.col("MyDate") >= "2020-01-01")

does not work like it does in pandas.

I found a workaround

df.filter(pl.col("MyDate") >= pl.datetime(2020,1,1))

but this does not solve a problem if I need to use string variables.

Answer 1

You can turn the string into a date type e.g. with .str.to_date()

Building on the example above:

import polars as pl
from datetime import datetime

df = pl.DataFrame({
    "dates": [datetime(2021, 1, 1), datetime(2021, 1, 2), datetime(2021, 1, 3)],
    "vals": range(3)
})

df.filter(pl.col('dates') >= pl.lit(my_date_str).str.to_date())

shape: (2, 2)
┌─────────────────────┬──────┐
│ dates               ┆ vals │
│ ---                 ┆ ---  │
│ datetime[μs]        ┆ i64  │
╞═════════════════════╪══════╡
│ 2021-01-02 00:00:00 ┆ 1    │
│ 2021-01-03 00:00:00 ┆ 2    │
└─────────────────────┴──────┘