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Introduction

Python to R translation of 30 essential Pandas methods introduced by Avi Chawla in The Only 30 Methods You Should Master To Become A Pandas Pro published on TowardsDataScience.

Set up

# enable python in RMarkdown
library(reticulate)

Method #16-17. Adding New Column(s)

Python

To add a column based on simple calculation of existing columns, we could either do the calculation directly (first chunk below) or use the assign() method.

import pandas as pd

df = pd.DataFrame({'col1': [1,2],
                   'col2': [3,4]})
# direct calculation
df2 = df.copy()
df2['col3'] = df['col1'] + df['col2'] 
df2
   col1  col2  col3
0     1     3     4
1     2     4     6
# use assign() method
df2 = df.assign(col3 = df['col1'] + df['col2'] )
df2
   col1  col2  col3
0     1     3     4
1     2     4     6

R

In R, mutate() function handels these tasks with ease

library(dplyr)

df <- py$df #load the df object created in Python above

df2 <- df |>  
  mutate(col3 = col1 + col2)
df2
  col1 col2 col3
1    1    3    4
2    2    4    6

Bonus: More complex situations

Now let’s try some slightly more complex calculations and/or create more than one columns in one go as well.

Create multiple columns in one go

Python

(df
  .assign(col3 = lambda x: x.col1*2 + x.col2)
  .assign(col4 = lambda x: (x.col1/x.col2 * 100).round(3)))
   col1  col2  col3    col4
0     1     3     5  33.333
1     2     4     8  50.000

R

To accomplish a similar task in R, we will continue to use mutate()

df |>  
  mutate(col3 = col1*2 + col2,
         col4 = round(col1/col2 * 100, 3))
  col1 col2 col3   col4
1    1    3    5 33.333
2    2    4    8 50.000

Mean across columns

Python

df['row_mean'] = df.iloc[:,0:].mean(axis=1) # all columns
print(df)
   col1  col2  row_mean
0     1     3       2.0
1     2     4       3.0
df['row_mean'] = df.iloc[:,0:2].mean(axis=1) # specify columns by range
print(df)
   col1  col2  row_mean
0     1     3       2.0
1     2     4       3.0
df['row_mean'] = df.iloc[:,[0,1]].mean(axis=1) # specify columns by position
print(df)
   col1  col2  row_mean
0     1     3       2.0
1     2     4       3.0

R

df |> mutate(row_mean = df |> rowMeans()) # all columns
  col1 col2 row_mean
1    1    3        2
2    2    4        3
df |> mutate(row_mean = df |> select(1:2) |> rowMeans()) # specify columns by range
  col1 col2 row_mean
1    1    3        2
2    2    4        3
df |> mutate(row_mean = df |> select(1,2) |> rowMeans()) # specify columns by position
  col1 col2 row_mean
1    1    3        2
2    2    4        3

Encoding categorical columns

Python

The map function is pretty helpful in the scenario

df = pd.DataFrame({'gender':['male', 'female', 'male', 'female']})
# add a column with gender encoding
df['is_male'] = df['gender'].map({'male': 1, 'female': 0})
print(df)
   gender  is_male
0    male        1
1  female        0
2    male        1
3  female        0

R

Of course, tihs task is easy with dplyr

df <- py$df
df |> 
  mutate(is_male = ifelse(gender == 'male', 1, 0))
  gender is_male
1   male       1
2 female       0
3   male       1
4 female       0

sessionInfo()
R version 4.2.1 (2022-06-23 ucrt)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 10 x64 (build 19045)

Matrix products: default

locale:
[1] LC_COLLATE=English_Australia.utf8  LC_CTYPE=English_Australia.utf8   
[3] LC_MONETARY=English_Australia.utf8 LC_NUMERIC=C                      
[5] LC_TIME=English_Australia.utf8    

attached base packages:
[1] stats     graphics  grDevices datasets  utils     methods   base     

other attached packages:
[1] dplyr_1.1.2     reticulate_1.30

loaded via a namespace (and not attached):
 [1] Rcpp_1.0.11       pillar_1.9.0      compiler_4.2.1    bslib_0.5.0      
 [5] later_1.3.1       jquerylib_0.1.4   git2r_0.32.0      workflowr_1.7.0  
 [9] tools_4.2.1       digest_0.6.33     lattice_0.20-45   jsonlite_1.8.7   
[13] evaluate_0.21     lifecycle_1.0.3   tibble_3.2.1      png_0.1-8        
[17] pkgconfig_2.0.3   rlang_1.1.1       Matrix_1.4-1      cli_3.6.1        
[21] rstudioapi_0.15.0 yaml_2.3.7        xfun_0.39         fastmap_1.1.1    
[25] withr_2.5.0       stringr_1.5.0     knitr_1.43        generics_0.1.3   
[29] fs_1.6.2          vctrs_0.6.3       sass_0.4.7        tidyselect_1.2.0 
[33] grid_4.2.1        rprojroot_2.0.3   here_1.0.1        glue_1.6.2       
[37] R6_2.5.1          fansi_1.0.4       rmarkdown_2.23    magrittr_2.0.3   
[41] whisker_0.4.1     promises_1.2.0.1  htmltools_0.5.5   renv_1.0.0       
[45] httpuv_1.6.11     utf8_1.2.3        stringi_1.7.12    cachem_1.0.8