英文:
How do I apply and/or boolean logic on Polars .when conditionals?
问题
以下是您请求的翻译：
Let's start with my dataframe. It has 2 columns, src and tgt. When tgt is not null and src is not "?", I want to set tgt=src.
让我们从我的数据框开始。它有2列，src 和 tgt。当 tgt 不为空 并且 src 不是 "?" 时，我想将 tgt 设置为 src。
should then give, with an alias to newtgt
应该如下，使用别名 newtgt：
I can check the not null and I can check == "?". How do I combine them? I tried and, &, and &&, none of which worked.
我可以检查非空，也可以检查 == "?"。如何将它们组合起来？我尝试了 and、& 和 &&，但都不起作用。
What I have so far, including error messages:
到目前为止，我的代码如下，包括错误消息：
output:
输出：
英文:
Let's start with my dataframe. It has 2 columns, src and tgt. When tgt is not null and src is not "?" , I want to set tgt=src.
┌─────┬──────┐│ tgt ┆ src ││ --- ┆ --- ││ str ┆ str │╞═════╪══════╡│ a ┆ !a ││ ? ┆ b ││ ? ┆ null │└─────┴──────┘
should then give, with an alias to newtgt
┌─────┬──────┬────────┐│ tgt ┆ src ┆ newtgt ││ --- ┆ --- ┆ --- ││ str ┆ str ┆ str │╞═════╪══════╪════════╡│ a ┆ !a ┆ a ││ ? ┆ b ┆ b ││ ? ┆ null ┆ ? │└─────┴──────┴────────┘
I can check the not null and I can check == "?". How do I combine them? I tried and, & and &&, none of which worked.
What I have so far, including error messages:
import polars as pldf = pl.from_dict(dict(tgt=["a","?","?"],src=["!a","b",None]))print("\ndf before:\n",df)df2 = df.with_columns(pl.when(pl.col("src").is_not_null()).then(pl.col("src")).otherwise(pl.col("tgt")).alias("newtgt"))print("\ndf2 check if src not null:\n",df2)df2 = df.with_columns(pl.when(pl.col("tgt") == "?").then(pl.col("src")).otherwise(pl.col("tgt")).alias("newtgt"))print("\ndf2 if check tgt already known:\n",df2)try:print("\n\ncheck both with `and`: ")df2 = df.with_columns(pl.when(pl.col("tgt") == "?" and pl.col("src").is_not_null()).then(pl.col("src")).otherwise(pl.col("tgt")).alias("newtgt"))except (ValueError,) as e:print("\nnot happy with `and`:\n ", e)try:print("\n\ncheck both with `&`: ")df2 = df.with_columns(pl.when(pl.col("tgt") == "?" & pl.col("src").is_not_null()).then(pl.col("src")).otherwise(pl.col("tgt")).alias("newtgt"))except (pl.exceptions.InvalidOperationError,) as e:print("\nnot happy with `&`:\n ", e)
output:
df before:shape: (3, 2)┌─────┬──────┐│ tgt ┆ src ││ --- ┆ --- ││ str ┆ str │╞═════╪══════╡│ a ┆ !a ││ ? ┆ b ││ ? ┆ null │└─────┴──────┘df2 check if src not null:shape: (3, 3)┌─────┬──────┬────────┐│ tgt ┆ src ┆ newtgt ││ --- ┆ --- ┆ --- ││ str ┆ str ┆ str │╞═════╪══════╪════════╡│ a ┆ !a ┆ !a ││ ? ┆ b ┆ b ││ ? ┆ null ┆ ? │└─────┴──────┴────────┘df2 if check tgt already known:shape: (3, 3)┌─────┬──────┬────────┐│ tgt ┆ src ┆ newtgt ││ --- ┆ --- ┆ --- ││ str ┆ str ┆ str │╞═════╪══════╪════════╡│ a ┆ !a ┆ a ││ ? ┆ b ┆ b ││ ? ┆ null ┆ null │└─────┴──────┴────────┘check both with `and`:not happy with `and`:Since Expr are lazy, the truthiness of an Expr is ambiguous. Hint: use '&' or '|' to logically combine Expr, not 'and'/'or', and use 'x.is_in([y,z])' instead of 'x in [y,z]' to check membership.check both with `&`:not happy with `&`:`bitand` operation not supported for dtype `str`
答案1
得分: 1
在polars中，您需要为复杂和/或表达式的每个部分加括号，以避免模糊错误。正如该错误消息所暗示的那样，&也必须用于and：
df.with_columns(pl.when((pl.col("tgt") == "?") & (pl.col("src").is_not_null())).then(pl.col("src")).otherwise(pl.col("tgt")).alias("newtgt"))
shape: (3, 3)┌─────┬──────┬────────┐│ tgt ┆ src ┆ newtgt ││ --- ┆ --- ┆ --- ││ str ┆ str ┆ str │╞═════╪══════╪════════╡│ a ┆ !a ┆ a ││ ? ┆ b ┆ b ││ ? ┆ null ┆ ? │└─────┴──────┴────────┘
另一个等效的选项是pl.all(expr1, expr2, ...)。
英文:
In polars you need to parenthesize each part of a complex and/or expression to avoid that ambiguous error. As that error message implies, & is required as well over and:
df.with_columns(pl.when((pl.col("tgt") == "?") & (pl.col("src").is_not_null())).then(pl.col("src")).otherwise(pl.col("tgt")).alias("newtgt"))
shape: (3, 3)┌─────┬──────┬────────┐│ tgt ┆ src ┆ newtgt ││ --- ┆ --- ┆ --- ││ str ┆ str ┆ str │╞═════╪══════╪════════╡│ a ┆ !a ┆ a ││ ? ┆ b ┆ b ││ ? ┆ null ┆ ? │└─────┴──────┴────────┘
Another equivalent option is pl.all(expr1, expr2, ...)
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