Pivot longer-ing in Polars

The Polars equivalent for pivot_longer from dplyR is melt.

dplyrR example (R)

suppressPackageStartupMessages(
  library('tidyverse')
)

otter_data = read_csv(
  'https://raw.githubusercontent.com/jcoliver/learn-r/gh-pages/data/otter-mandible-data.csv',
  col_types = cols()
)

otter_data |>
  pivot_longer(cols = matches('m\\d')) |>
  head() |>
  gt::gt()

species	museum	accession	name	value
A. cinerea	AMNH	101458	m1	15.100
A. cinerea	AMNH	101458	m2	27.790
A. cinerea	AMNH	101458	m3	21.885
A. cinerea	AMNH	101458	m4	13.010
A. cinerea	AMNH	101458	m5	10.500
A. cinerea	AMNH	101458	m6	61.635

Polars example (Python)

import polars as pl
from great_tables import GT

(
  pl.read_csv(
    'https://raw.githubusercontent.com/jcoliver/learn-r/gh-pages/data/otter-mandible-data.csv',
    null_values='NA'
  )
  .melt(id_vars=['species', 'museum', 'accession'])
  .head()
  .pipe(lambda df_: GT(df_))
)

species	museum	accession	variable	value
A. cinerea	AMNH	101458	m1	15.1
A. cinerea	AMNH	101461	m1	12.74
A. cinerea	AMNH	101466	m1	12.425
A. cinerea	AMNH	101635	m1	13.4
A. cinerea	AMNH	101459	m1	14.4