python - Map values in dataframe columns from dictionary with list as value

Question

I am trying to map values to dataframe columns from a dictionary. Here is the code:

# 
import pandas as pd
region_dict = {'Russia':['Europe','Eastern Europe'], 
               'South Korea':['Asia','Easter Asia'],
               'Iran':['Asia','Southern Asia'], 
               'North Korea':['Asia','Eastern Asia']}
region_dict
#> {'Russia': ['Europe', 'Eastern Europe'],
   'South Korea': ['Asia', 'Eastern Asia'],
   'Iran': ['Asia', 'Southern Asia'],
   'North Korea': ['Asia', 'Eastern Asia']}
    
df = pd.DataFrame({'Country':['Russia', 'Iran', 'South Korea','USA'],
                   'continent':['NaN','NaN','NaN','Americas'],
                   'sub_region':['NaN','NaN','NaN','Northern America']})
df
#>      Country  continent        sub_region
0       Russia         NaN               NaN
1         Iran         NaN               NaN
2  South Korea         NaN               NaN
3          USA    Americas  Northern America

Desired Output:

#>      Country  Continent  Sub_region
0       Russia   Europe     Eastern Europe  
1         Iran   Asia       Southern Asia
2  South Korea   Asia       Eastern Asia
3          USA   NaN        NaN

I tried

df[['continent','sub_region']] = df['country'].map(region_dict)

***Error***
ValueError: shape mismatch: value array of shape (20036,) could not be broadcast to indexing result of shape (2,20036)

This way works when the dictionary is in the form

region_dict = {'Russia':'Asia'}

and I map as

df['continent'] = df['country'].map(region_dict)

Questions

How to map multiple columns from a dictionary having list of multiple items as values?
If I want to add only the sub_region column to the df and want to add region_dict['Russia'][1] to the df column, how shall I do it?

anky · Accepted Answer · 2021-01-20 15:07:16Z

1

You should convert the mapped series of lists to a df and then assign:

df[['continent','sub_region']] = pd.DataFrame(df['Country'].map(region_dict).tolist())

answered Jan 20, 2021 at 15:07

anky

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3 Comments

rahul-ahuja Over a year ago

Your solution worked. But when I tried to apply it to a larger dataframe that already had 2 columns for continent and sub_region, I got the error : ValueError: Columns must be same length as key. I have added to the question to reflect that scenario.

rahul-ahuja Over a year ago

Even to the original question, when I run pd.DataFrame(df['Country'].map(region_dict).tolist()), I get this error : TypeError: object of type 'float' has no len()

anky Over a year ago

@rahul-ahuja that is because you have non matching members, try assigning pd.DataFrame(df['Country'].map(region_dict).dropna().tolist())

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