Adding values across multiple columns in polars

sum_horizontal

Most dataframe libraries are excellent at performing columnar operations, such as adding or multiplying values within a single column. However, there are times when you may want to perform such operations across multiple columns. Below is a dataframe of Apple stock values.

shape: (4, 5)

Date	Open	High	Low	Close
str	f64	f64	f64	f64
"2024-08-12"	216.070007	219.509995	215.600006	217.529999
"2024-08-13"	219.009995	221.889999	219.009995	221.270004
"2024-08-14"	220.570007	223.029999	219.699997	221.720001
"2024-08-15"	224.600006	225.350006	222.759995	224.720001

Say we want to create another column called Sum_OHLC that adds the values from the Open to Close columns.

The manual way

Here’s the manual approach to add the values across columns:

(df
 .with_columns((pl.col('Open') + pl.col('High') + pl.col('Low') + pl.col('Close'))
               .alias('Sum_OHLC'))
 )

shape: (4, 6)

Date	Open	High	Low	Close	Sum_OHLC
str	f64	f64	f64	f64	f64
"2024-08-12"	216.070007	219.509995	215.600006	217.529999	868.710007
"2024-08-13"	219.009995	221.889999	219.009995	221.270004	881.179993
"2024-08-14"	220.570007	223.029999	219.699997	221.720001	885.020004
"2024-08-15"	224.600006	225.350006	222.759995	224.720001	897.430008

The efficient way

And here’s the idiomatic and more efficient way to do it:

(df
 .with_columns(pl.sum_horizontal('Open', 'High', 'Low', 'Close')
               .alias('Sum_OHLC'))
 )

shape: (4, 6)

Date	Open	High	Low	Close	Sum_OHLC
str	f64	f64	f64	f64	f64
"2024-08-12"	216.070007	219.509995	215.600006	217.529999	868.710007
"2024-08-13"	219.009995	221.889999	219.009995	221.270004	881.179993
"2024-08-14"	220.570007	223.029999	219.699997	221.720001	885.020004
"2024-08-15"	224.600006	225.350006	222.759995	224.720001	897.430008

The showing off way

Or if you want to impress the hiring manager in a coding interview, you can do it like this.

(df
 .with_columns(pl.sum_horizontal(pl.nth(list(range(1,5))))
               .alias('Sum_OHLC'))
 )

shape: (4, 6)

Date	Open	High	Low	Close	Sum_OHLC
str	f64	f64	f64	f64	f64
"2024-08-12"	216.070007	219.509995	215.600006	217.529999	868.710007
"2024-08-13"	219.009995	221.889999	219.009995	221.270004	881.179993
"2024-08-14"	220.570007	223.029999	219.699997	221.720001	885.020004
"2024-08-15"	224.600006	225.350006	222.759995	224.720001	897.430008

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