Check if Python Polars DataFrame row value exists within a defined list-CodePudding

I'm really new to Polars (v0.15.8)...so I really don't know what I'm doing.

I have a Dataframe and I would like to check whether each row from a column exists within a separately defined list.

For example, here is my list:

list_animal = ['cat', 'mouse', 'dog', 'sloth', 'zebra']

and here is my Dataframe:

df = pl.DataFrame([
        pl.Series('thing', ['cat', 'plant', 'mouse', 'dog', 'sloth', 'zebra', 'shoe']),
        pl.Series('isAnimal', [None, None, None, None, None, None, None]),
])

...which looks like this:

I would like the df to end up like:

I'm struggling my way through some examples and the Polars documentation. I have found two options:

use the pl.when function:

df = (df.with_column(
     pl.when(
         (pl.col("thing") in list_animal)
     )
     .then(True)
     .otherwise(False)
     .alias("isAnimal2")
))

However, I get an error:

ValueError: Since Expr are lazy, the truthiness of an Expr is ambiguous. Hint: use '&' or '|' to chain Expr together, not and/or.

or,

Using the docs here, I tried to follow the examples to apply an expression on the elements of a list. I couldn't make it work, but I tried this:

chk_if_true = pl.element() in list_animal

df.with_column(
    pl.col("thing").arr.eval(chk_if_true, parallel=True).alias("isAnimal2")

)

...which gave me this error:

SchemaError: Series of dtype: Utf8 != List

I would appreciate any advice; thanks!

CodePudding user response：

You're looking for .is_in()

>>> df.with_column(pl.col("thing").is_in(list_animal).alias("isAnimal2"))
shape: (7, 3)
┌───────┬──────────┬───────────┐
│ thing | isAnimal | isAnimal2 │
│ ---   | ---      | ---       │
│ str   | f64      | bool      │
╞═══════╪══════════╪═══════════╡
│ cat   | null     | true      │
├───────┼──────────┼───────────┤
│ plant | null     | false     │
├───────┼──────────┼───────────┤
│ mouse | null     | true      │
├───────┼──────────┼───────────┤
│ dog   | null     | true      │
├───────┼──────────┼───────────┤
│ sloth | null     | true      │
├───────┼──────────┼───────────┤
│ zebra | null     | true      │
├───────┼──────────┼───────────┤
│ shoe  | null     | false     │
└───────┴──────────┴───────────┘