Pandas converting columns to rows

Question

I have a dataframe with columns like this -

Name Id 2019col1 2019col2 2019col3 2020col1 2020col2 2020col3 2021col1 2021Ccol2 2021Ccol3

That is, the columns are repeated for each year. I want to take the year out and make it a column, so that the final dataframe looks like -

 Name Id Year col1 col2 col3

Is there a way in pandas to achieve something like this?

jezrael · Accepted Answer · 2019-10-23 07:16:59Z

3

Use wide_to_long, but before change order years to end of columns names like 2019col1 to col12019 in list comprehension:

print (df)
  Name   Id  2019col1  2019col2  2019col3  2020col1  2020col2  2020col3  \
0    a  456         4         5         6         2         3         4   

   2021col1  2021col2  2021col3  
0         5         2         1  

df.columns = [x[4:] + x[:4] if x[:4].isnumeric() else x for x in df.columns]

df = (pd.wide_to_long(df.reset_index(), 
                      ['col1','col2', 'col3'],
                      i='index',
                      j='Year').reset_index(level=0, drop=True).reset_index())
print (df)

   Year   Id Name  col1  col2  col3
0  2019  456    a     4     5     6
1  2020  456    a     2     3     4
2  2021  456    a     5     2     1

answered Oct 23, 2019 at 7:16

jezrael

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