Can´t copy tupel from one dataframe into another (Length of values does not match length of index)

Question

I want to create columns in a dataframe (df_joined) that contains as values tupels from a second df (df_tupels). The tupels are (10,50) and (20,60).

I tried various approaches to create it but I get the same error message: "Length of values (2) does not match length of index (4)". Seems I am not understanding a concept here.

This is the desired end state:

       Season     NY        Berlin
Cities          
NY      spring  (10, 50)    (20, 60)
NY      summer  (10, 50)    (20, 60)
Berlin  spring  (10, 50)    (20, 60)
Berlin  summer  (10, 50)    (20, 60)

data_ = {'Cities': ['NY', 'NY', 'Berlin', 'Berlin'], 'Season': ['spring','summer', 'spring', 'summer'], 'NY': ['(10, 50)', '(10, 50)', '(10, 50)', '(10, 50)'], 'Berlin': ['(20, 60)', '(20, 60)', '(20, 60)', '(20, 60)']}
df_intended = pd.DataFrame(data)
df_intended.set_index('Cities', inplace=True)

Code example is:

import pandas as pd

#create df in which tupels should be copied into new columns:
data = {'Cities': ['NY', 'NY', 'Berlin', 'Berlin'], 'Season': ['spring','summer', 'spring', 'summer']}
df_joined = pd.DataFrame(data)
df_joined.set_index('Cities', inplace=True)

# create source df (df_tupels)
df_tupels = pd.DataFrame({'Cities': ['NY', 'Berlin'], 'Lat': [10, 20], 'Long': [50, 60]})
df_tupels['tupels'] = df_tupels[['Lat', 'Long']].apply(tuple, axis=1)
df_tupels.set_index('Cities', inplace=True)

# trying to create new city columns from index and filling with tupels of df_tupels.
for city in df_tupels.index:
    df_joined[city] = df_tupels['tupels'].loc[city]

    #Following solutions don´t work here either
    #df_joined.loc[:, city] = df_tupels['tupels'].loc[city]
    #df_joined.insert(0, city, df_tupels['tupels'].loc[city])

Error message: ValueError: Length of values (2) does not match length of index (4)

I´ve notice posts with similar error messages but could not use them for my problem here.

Why isn´t the new dataframe column just filled with the respective tupel? What am I missing?

Answer 1

You need to create a list of tuple that matches the dataframe length.

for city in df_tupels.index:
    df_joined[city] = [df_tupels['tupels'].loc[city]] * len(df_joined)

print(df)

        Season        NY    Berlin
Cities
NY      spring  (10, 50)  (20, 60)
NY      summer  (10, 50)  (20, 60)
Berlin  spring  (10, 50)  (20, 60)
Berlin  summer  (10, 50)  (20, 60)