Polars, python, how to change the number of conditions inputted when making a new column - Stack Overflow

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I have large datasets (ranging from 100k - 4 million rows) where I am looking for different relevant codes across multiple columns. For example, if I wanted to identify each row which has some start to a string '302' I would do:

import polars as pl

df = pl.DataFrame({
'Codes_1': ['302E513', '301E513', '302E512'],
'Codes_2': ['303E513', '306E510', '302E512']}).lazy()

conditions = ['302E513', '306E510']
column_names = ['Codes_1', 'Codes_2']

#create new column
df = df.with_columns(
   pl.when(pl.any_horizontal( 
       pl.col(column_names).str.starts_with(conditions[0]),
       pl.col(column_names).str.starts_with(conditions[1])))
   .then(1.0)
   .otherwise(0.0)
   .alias('Column_name')
)

It is really annoying when I am looking for say 4 codes instead of 2 to have to type in each of the codes to form my new column:

import polars as pl

df = pl.DataFrame({
'Codes_1': ['302E513', '301E513', '302E512'],
'Codes_2': ['303E513', '306E510', '302E512']}).lazy()

conditions = ['302E513', '306E510', '5164E23', '302E514']
column_names = ['Codes_1', 'Codes_2']

#create new column
df = df.with_columns(
   pl.when(pl.any_horizontal(
       #Tedious part 
       pl.col(column_names).str.starts_with(conditions[0]),
       pl.col(column_names).str.starts_with(conditions[1]),
       pl.col(column_names).str.starts_with(conditions[2]),
       pl.col(column_names).str.starts_with(conditions[3])
))
   .then(1.0)
   .otherwise(0.0)
   .alias('Column_name')
)

I know that this can be done with pandas by updating a mask with a for loop

import pandas as pd

df = pd.DataFrame({
'Codes_1': ['302E513', '301E513', '302E512'],
'Codes_2': ['303E513', '306E510', '302E512']})

conditions = ['302E513', '306E510']
column_names = ['Codes_1', 'Codes_2']

#loop to create new column
mask = False
for code in conditions:
   mask |= df[column_names].eq(code).any(axis=1)

df['Column_name'] = 0.0
df.loc[mask, 'Column_name'] = 1.0
print(df['Column_name'])

And I could change the number of conditions to any number and this code would execute. However, I would much rather use polars as it is faster and does not overflow the RAM on my machine for larger datasets. Any help is appreciated.

I have large datasets (ranging from 100k - 4 million rows) where I am looking for different relevant codes across multiple columns. For example, if I wanted to identify each row which has some start to a string '302' I would do:

import polars as pl

df = pl.DataFrame({
'Codes_1': ['302E513', '301E513', '302E512'],
'Codes_2': ['303E513', '306E510', '302E512']}).lazy()

conditions = ['302E513', '306E510']
column_names = ['Codes_1', 'Codes_2']

#create new column
df = df.with_columns(
   pl.when(pl.any_horizontal( 
       pl.col(column_names).str.starts_with(conditions[0]),
       pl.col(column_names).str.starts_with(conditions[1])))
   .then(1.0)
   .otherwise(0.0)
   .alias('Column_name')
)

It is really annoying when I am looking for say 4 codes instead of 2 to have to type in each of the codes to form my new column:

import polars as pl

df = pl.DataFrame({
'Codes_1': ['302E513', '301E513', '302E512'],
'Codes_2': ['303E513', '306E510', '302E512']}).lazy()

conditions = ['302E513', '306E510', '5164E23', '302E514']
column_names = ['Codes_1', 'Codes_2']

#create new column
df = df.with_columns(
   pl.when(pl.any_horizontal(
       #Tedious part 
       pl.col(column_names).str.starts_with(conditions[0]),
       pl.col(column_names).str.starts_with(conditions[1]),
       pl.col(column_names).str.starts_with(conditions[2]),
       pl.col(column_names).str.starts_with(conditions[3])
))
   .then(1.0)
   .otherwise(0.0)
   .alias('Column_name')
)

I know that this can be done with pandas by updating a mask with a for loop

import pandas as pd

df = pd.DataFrame({
'Codes_1': ['302E513', '301E513', '302E512'],
'Codes_2': ['303E513', '306E510', '302E512']})

conditions = ['302E513', '306E510']
column_names = ['Codes_1', 'Codes_2']

#loop to create new column
mask = False
for code in conditions:
   mask |= df[column_names].eq(code).any(axis=1)

df['Column_name'] = 0.0
df.loc[mask, 'Column_name'] = 1.0
print(df['Column_name'])

And I could change the number of conditions to any number and this code would execute. However, I would much rather use polars as it is faster and does not overflow the RAM on my machine for larger datasets. Any help is appreciated.

• python
• python-polars

Share Improve this question Follow edited Dec 3, 2024 at 19:43 jqurious 20.9k44 gold badges1919 silver badges3535 bronze badges asked Dec 3, 2024 at 18:24 zebra_zach_12345zebra_zach_12345 3333 bronze badges

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1 Answer 1

Sorted by: Reset to default 2

You could replace the multiple str.starts_with with a single regex and str.contains:

df.with_columns(
   pl.when(pl.any_horizontal(
       pl.col(column_names).str.contains(f"^({'|'.join(conditions)})"),
))
   .then(1.0)
   .otherwise(0.0)
   .alias('Column_name')
)

Or use a loop:

df.with_columns(
   pl.when(pl.any_horizontal(
       pl.col(column_names).str.starts_with(c)
        for c in conditions
))
   .then(1.0)
   .otherwise(0.0)
   .alias('Column_name')
)

Intermediate:

# f"^({'|'.join(conditions)})"
'^(302E513|306E510|5164E23|302E514)'

Output (non-lazy):

┌─────────┬─────────┬─────────────┐
│ Codes_1 ┆ Codes_2 ┆ Column_name │
│ ---     ┆ ---     ┆ ---         │
│ str     ┆ str     ┆ f64         │
╞═════════╪═════════╪═════════════╡
│ 302E513 ┆ 303E513 ┆ 1.0         │
│ 301E513 ┆ 306E510 ┆ 1.0         │
│ 302E512 ┆ 302E512 ┆ 0.0         │
└─────────┴─────────┴─────────────┘

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