So in python Polars
I can add one or more columns to make a new column by using an expression something like
frame.with_column((pl.col('colname1') + pl.col('colname2').alias('new_colname')))
However, if I have all the column names in a list is there a way to sum all the columns in that list and create a new column based on the result ?
Thanks
sum expr supports horizontal summing. From the docs,
List[Expr] -> aggregate the sum value horizontally.
Sample code for ref,
import polars as pl
df = pl.DataFrame({"a": [1, 2, 3], "b": [1, 2, None]})
print(df)
This results in something like,
shape: (3, 2)
┌─────┬──────┐
│ a ┆ b │
│ --- ┆ --- │
│ i64 ┆ i64 │
╞═════╪══════╡
│ 1 ┆ 1 │
├╌╌╌╌╌┼╌╌╌╌╌╌┤
│ 2 ┆ 2 │
├╌╌╌╌╌┼╌╌╌╌╌╌┤
│ 3 ┆ null │
└─────┴──────┘
On this you can do something like,
cols = ["a", "b"]
df2 = df.select(pl.sum([pl.col(i) for i in cols]).alias('new_colname'))
print(df2)
Which will result in,
shape: (3, 1)
┌──────┐
│ sum │
│ --- │
│ i64 │
╞══════╡
│ 2 │
├╌╌╌╌╌╌┤
│ 4 │
├╌╌╌╌╌╌┤
│ null │
└──────┘