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Introduction

Provide a 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)

Create the dataframe in Python

import pandas as pd

df = pd.DataFrame([[6, 5,  10], 
                   [5, 8,  6], 
                   [3, 10, 4]], 
                  columns = ["Maths", "Science", "English"],
                  index = ["John", "Mark", "Peter"])

print(df)
       Maths  Science  English
John       6        5       10
Mark       5        8        6
Peter      3       10        4

Load the dataframe into R

We notice that the index has been passed on to the dataframe in R.

df <- py$df #access df as saved in Python(py) above

print(df)
      Maths Science English
John      6       5      10
Mark      5       8       6
Peter     3      10       4

Method #20. Filtering a DataFrame3: Selecting by Label

Python

with .loc[], we can select by labels as follows

df.loc['John'] # select one specific row
Maths       6
Science     5
English    10
Name: John, dtype: int64
df.loc['John','Maths'] # select one specific row and column
6
df.loc[['John','Mark'],['Maths','Science']] # select a list of rows and columns
      Maths  Science
John      6        5
Mark      5        8

R

To do this in base R is fairly simple as shown below

df['John',] # select one specific row
     Maths Science English
John     6       5      10
df['John','Maths'] # select one specific row and column
[1] 6
df[c('John','Mark'),c('Maths','Science')]  # select a list of rows and columns
     Maths Science
John     6       5
Mark     5       8

Bonus: select columns by value

Imagine a dataframe like below, we have scores of multiple students and would like to identify all students who score 80 or above in all three courses.

data = {
  'subject': ['math', 'science', 'english'],
  'John': [80, 95, 78],
  'Alex': [90, 67, 84],
  'Angela': [87, 86, 90],
  'Bella': [78, 91, 80],
  'Trice': [87, 75, 91]
}

df = pd.DataFrame(data)

df.set_index('subject', inplace = True)

df
         John  Alex  Angela  Bella  Trice
subject                                  
math       80    90      87     78     87
science    95    67      86     91     75
english    78    84      90     80     91

python

In python, loc can be used to identify students who score higher than 80 in each course.

math_80 = df.loc[:, df.loc['math']>80].columns
science_80 = df.loc[:, df.loc['science']>80].columns
english_80 = df.loc[:, df.loc['english']>80].columns
print(f'{math_80}\n{science_80}\n{english_80}')
Index(['Alex', 'Angela', 'Trice'], dtype='object')
Index(['John', 'Angela', 'Bella'], dtype='object')
Index(['Alex', 'Angela', 'Trice'], dtype='object')

We can turn the lists into set then use set.intersection to find common elements in it.

all_rounder = list(set.intersection(*map(set, [math_80, science_80, english_80])))
all_rounder
['Angela']

R

To do this in r, select_if which is a variation/extension of select introduced in method #19 can be used to identify students who score above 80 in each course.

library(dplyr)
df = py$df

math_80 <- df |> select_if(df['math',] > 80) |> colnames()
science_80 <- df |> select_if(df['science',] > 80) |> colnames()
english_80 <- df |> select_if(df['english',] > 80) |> colnames()

Then use intersect to identify common elements.

all_rounder = Reduce(intersect, list(math_80, science_80, english_80))
all_rounder
[1] "Angela"

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   glue_1.6.2        R6_2.5.1         
[37] fansi_1.0.4       rmarkdown_2.23    magrittr_2.0.3    whisker_0.4.1    
[41] promises_1.2.0.1  htmltools_0.5.5   renv_1.0.0        httpuv_1.6.11    
[45] utf8_1.2.3        stringi_1.7.12    cachem_1.0.8