Dplyr’s across: Replicating within Pandas

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Dplyr’s across: Replicating within Pandas#

dplyr has the across function, which is meant to make column wise processing easy. Pandas has always supported column-wise operations, and in a relatively simple manner.

This article aims to replicate solutions in the dplyr column-wise operations vignette with Pandas.

Let’s load in the relevant libraries

import pandas as pd
import numpy as np
import sys

print(" pandas version :", pd.__version__,"\n", 
      "numpy version :", np.__version__, "\n", 
      "python version :", sys.version)

 pandas version : 2.2.2 
 numpy version : 2.0.2 
 python version : 3.10.14 | packaged by conda-forge | (main, Mar 20 2024, 12:51:49) [Clang 16.0.6 ]

url = "https://raw.githubusercontent.com/tidyverse/dplyr/main/data-raw/starwars.csv"
starwars = pd.read_csv(url)
starwars.head()
name height mass hair_color skin_color eye_color birth_year sex gender homeworld species films vehicles starships
0 Luke Skywalker 172.0 77.0 blond fair blue 19.0 male masculine Tatooine Human A New Hope, The Empire Strikes Back, Return of... Snowspeeder, Imperial Speeder Bike X-wing, Imperial shuttle
1 C-3PO 167.0 75.0 NaN gold yellow 112.0 none masculine Tatooine Droid A New Hope, The Empire Strikes Back, Return of... NaN NaN
2 R2-D2 96.0 32.0 NaN white, blue red 33.0 none masculine Naboo Droid A New Hope, The Empire Strikes Back, Return of... NaN NaN
3 Darth Vader 202.0 136.0 none white yellow 41.9 male masculine Tatooine Human A New Hope, The Empire Strikes Back, Return of... NaN TIE Advanced x1
4 Leia Organa 150.0 49.0 brown light brown 19.0 female feminine Alderaan Human A New Hope, The Empire Strikes Back, Return of... Imperial Speeder Bike NaN 
# dplyr : 
# starwars %>% 
#   summarise(across(where(is.character), n_distinct))
(starwars
.select_dtypes('object')
.nunique(dropna=False))

name          87
hair_color    12
skin_color    31
eye_color     15
sex            5
gender         3
homeworld     49
species       38
films         24
vehicles      11
starships     16
dtype: int64

# dplyr :
# starwars %>% 
#   group_by(species) %>% 
#   filter(n() > 1) %>% 
#   summarise(across(c(sex, gender, homeworld), n_distinct))

grp = starwars.groupby('species')

(grp[['sex', 'gender', 'homeworld']]
 .nunique(dropna=False)
 .loc[grp.size().gt(1)]
 )
sex gender homeworld
species
Droid 1 2 3
Gungan 1 1 1
Human 2 2 15
Kaminoan 2 2 1
Mirialan 1 1 1
Twi'lek 2 2 1
Wookiee 1 1 1
Zabrak 1 1 2

Another approach is with the pipe function:

(starwars
.filter(['species', 'sex', 'gender', 'homeworld'])
.groupby('species')
.pipe(lambda df: df.nunique(dropna = False).loc[df.size().gt(1)])
)
sex gender homeworld
species
Droid 1 2 3
Gungan 1 1 1
Human 2 2 15
Kaminoan 2 2 1
Mirialan 1 1 1
Twi'lek 2 2 1
Wookiee 1 1 1
Zabrak 1 1 2 
# dplyr : 
# starwars %>% 
#   group_by(homeworld) %>% 
#   filter(n() > 1) %>% 
#   summarise(across(where(is.numeric), ~ mean(.x, na.rm = TRUE)))

# get the grouper
grp = starwars.set_index('homeworld').select_dtypes('number').groupby('homeworld')
# get the size:
n = grp.size()
# filter averages with the size:
grp.mean().loc[n.gt(1)]
height mass birth_year
homeworld
Alderaan 176.333333 64.000000 43.000000
Corellia 175.000000 78.500000 25.000000
Coruscant 173.666667 50.000000 91.000000
Kamino 208.333333 83.100000 31.500000
Kashyyyk 231.000000 124.000000 200.000000
Mirial 168.000000 53.100000 49.000000
Naboo 177.272727 64.166667 55.000000
Ryloth 179.000000 55.000000 48.000000
Tatooine 169.800000 85.375000 54.644444

With the pipe function:

(starwars
.set_index('homeworld')
.select_dtypes('number')
.groupby('homeworld')
.pipe(lambda df: df.mean().loc[df.size().gt(1)])
)
height mass birth_year
homeworld
Alderaan 176.333333 64.000000 43.000000
Corellia 175.000000 78.500000 25.000000
Coruscant 173.666667 50.000000 91.000000
Kamino 208.333333 83.100000 31.500000
Kashyyyk 231.000000 124.000000 200.000000
Mirial 168.000000 53.100000 49.000000
Naboo 177.272727 64.166667 55.000000
Ryloth 179.000000 55.000000 48.000000
Tatooine 169.800000 85.375000 54.644444

An alternate approach, where the groupby is reused, is with pyjanitor’s get_columns function:

from janitor import get_columns
from pandas.api.types import is_numeric_dtype

grp = starwars.groupby('homeworld')
(grp
 .pipe(get_columns, is_numeric_dtype)
 .mean()
 .loc[grp.size().gt(1)]
 )
height mass birth_year
homeworld
Alderaan 176.333333 64.000000 43.000000
Corellia 175.000000 78.500000 25.000000
Coruscant 173.666667 50.000000 91.000000
Kamino 208.333333 83.100000 31.500000
Kashyyyk 231.000000 124.000000 200.000000
Mirial 168.000000 53.100000 49.000000
Naboo 177.272727 64.166667 55.000000
Ryloth 179.000000 55.000000 48.000000
Tatooine 169.800000 85.375000 54.644444 
# dplyr:
# starwars %>% distinct(across(contains("color")))
starwars.filter(like='color').drop_duplicates()
hair_color skin_color eye_color
0 blond fair blue
1 NaN gold yellow
2 NaN white, blue red
3 none white yellow
4 brown light brown
... ... ... ...
80 none pale white
82 black dark dark
83 brown light hazel
85 none none black
86 none none unknown

67 rows × 3 columns

# dplyr
# starwars %>% count(across(contains("color")), sort = TRUE)
starwars.filter(like='color').value_counts(dropna = False)

hair_color    skin_color  eye_color
brown         light       brown        6
              fair        blue         4
none          grey        black        4
black         dark        brown        3
blond         fair        blue         3
                                      ..
none          dark        brown        1
              green       black        1
auburn, grey  fair        blue         1
none          green       red          1
NaN           white, red  red          1
Name: count, Length: 67, dtype: int64

# starwars %>% 
#   filter(if_any(everything(), ~ !is.na(.x)))
starwars.loc[starwars.notna().any(axis=1)]
name height mass hair_color skin_color eye_color birth_year sex gender homeworld species films vehicles starships
0 Luke Skywalker 172.0 77.0 blond fair blue 19.0 male masculine Tatooine Human A New Hope, The Empire Strikes Back, Return of... Snowspeeder, Imperial Speeder Bike X-wing, Imperial shuttle
1 C-3PO 167.0 75.0 NaN gold yellow 112.0 none masculine Tatooine Droid A New Hope, The Empire Strikes Back, Return of... NaN NaN
2 R2-D2 96.0 32.0 NaN white, blue red 33.0 none masculine Naboo Droid A New Hope, The Empire Strikes Back, Return of... NaN NaN
3 Darth Vader 202.0 136.0 none white yellow 41.9 male masculine Tatooine Human A New Hope, The Empire Strikes Back, Return of... NaN TIE Advanced x1
4 Leia Organa 150.0 49.0 brown light brown 19.0 female feminine Alderaan Human A New Hope, The Empire Strikes Back, Return of... Imperial Speeder Bike NaN
... ... ... ... ... ... ... ... ... ... ... ... ... ... ...
82 Finn NaN NaN black dark dark NaN male masculine NaN Human The Force Awakens NaN NaN
83 Rey NaN NaN brown light hazel NaN female feminine NaN Human The Force Awakens NaN NaN
84 Poe Dameron NaN NaN brown light brown NaN male masculine NaN Human The Force Awakens NaN X-wing
85 BB8 NaN NaN none none black NaN none masculine NaN Droid The Force Awakens NaN NaN
86 Captain Phasma NaN NaN none none unknown NaN female feminine NaN Human The Force Awakens NaN NaN

87 rows × 14 columns

# starwars %>% 
#   filter(if_any(everything(), ~ !is.na(.x)))
starwars.loc[starwars.notna().all(axis=1)]
name height mass hair_color skin_color eye_color birth_year sex gender homeworld species films vehicles starships
0 Luke Skywalker 172.0 77.0 blond fair blue 19.0 male masculine Tatooine Human A New Hope, The Empire Strikes Back, Return of... Snowspeeder, Imperial Speeder Bike X-wing, Imperial shuttle
9 Obi-Wan Kenobi 182.0 77.0 auburn, white fair blue-gray 57.0 male masculine Stewjon Human A New Hope, The Empire Strikes Back, Return of... Tribubble bongo Jedi starfighter, Trade Federation cruiser, Na...
10 Anakin Skywalker 188.0 84.0 blond fair blue 41.9 male masculine Tatooine Human The Phantom Menace, Attack of the Clones, Reve... Zephyr-G swoop bike, XJ-6 airspeeder Naboo fighter, Trade Federation cruiser, Jedi ...
12 Chewbacca 228.0 112.0 brown unknown blue 200.0 male masculine Kashyyyk Wookiee A New Hope, The Empire Strikes Back, Return of... AT-ST Millennium Falcon, Imperial shuttle
16 Wedge Antilles 170.0 77.0 brown fair hazel 21.0 male masculine Corellia Human A New Hope, The Empire Strikes Back, Return of... Snowspeeder X-wing
42 Darth Maul 175.0 80.0 none red yellow 54.0 male masculine Dathomir Zabrak The Phantom Menace Sith speeder Scimitar

Output for the above is different from the vignette’s because Pandas treats none as NaN, and dplyr does not (at least in the vignette)

Let’s look at another solution, from Stack Overflow:

url = "https://gist.githubusercontent.com/seankross/a412dfbd88b3db70b74b/raw/5f23f993cd87c283ce766e7ac6b329ee7cc2e1d1/mtcars.csv"
cars = pd.read_csv(url)
cars.head()
model mpg cyl disp hp drat wt qsec vs am gear carb
0 Mazda RX4 21.0 6 160.0 110 3.90 2.620 16.46 0 1 4 4
1 Mazda RX4 Wag 21.0 6 160.0 110 3.90 2.875 17.02 0 1 4 4
2 Datsun 710 22.8 4 108.0 93 3.85 2.320 18.61 1 1 4 1
3 Hornet 4 Drive 21.4 6 258.0 110 3.08 3.215 19.44 1 0 3 1
4 Hornet Sportabout 18.7 8 360.0 175 3.15 3.440 17.02 0 0 3 2 
# dplyr:
# dat <- group_by(mtcars, cyl) 
# summarize(dat, across(ends_with('p'), sum), across(ends_with('t'), mean))
aggs = {key:"mean" if key.endswith("t") else "sum" for key in cars if key.endswith(('p', 't'))}
cars.groupby('cyl').agg(aggs)
disp hp drat wt
cyl
4 1156.5 909 4.070909 2.285727
6 1283.2 856 3.585714 3.117143
8 4943.4 2929 3.229286 3.999214

An alternate approach, where the groupby is reused, is with pyjanitor’s get_columns function:

grp = cars.groupby('cyl')
summary = [get_columns(grp, '*p').sum(), get_columns(grp, '*t').mean()]
pd.concat(summary, axis = 1)
disp hp drat wt
cyl
4 1156.5 909 4.070909 2.285727
6 1283.2 856 3.585714 3.117143
8 4943.4 2929 3.229286 3.999214

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