pythonpandaspivotmelt

Reshaping a table, melting and pivoting with duplicate entries

import pandas as pd

data = [['4/04/2023','Floors','Tables','Roof','Paint','Paint'],['4/05/2023','Roof','Floors','Tables','Roof','Paint'],['4/06/2023','Paint','','Floors','Tables','Roof'],['4/07/2023','Roof','Paint','','Floors','Tables']]

df = pd.DataFrame(data, columns=['Date', 'Jim','Bob','Ed','James','Joe'])

df2 = df.melt(id_vars="Date", value_name='Items').dropna().reset_index(drop=True)

df3 = df2.pivot(index="Date", columns='Items', values='variable') df3 = df3[["Floors","Tables","Roof","Paint"]] #change the order

print(df)

print(df3)

I want this table: enter image description here

To look like this: enter image description here

I would like Pandas to detect duplicates and make an extra column where there are duplicates rather than throwing the following error:

raise ValueError("Index contains duplicate entries, cannot reshape")

ValueError: Index contains duplicate entries, cannot reshape

Solution

  • You can use:

    data = [['4/04/2023','Floors','Tables','Roof','Paint','Paint'],
        ['4/05/2023','Roof','Floors','Tables','Roof','Paint'],
        ['4/06/2023','Paint','','Floors','Tables','Roof'],
        ['4/07/2023','Roof','Paint','','Floors','Tables']]
df = pd.DataFrame(data, columns=['Date', 'Jim','Bob','Ed','James','Joe'])

out = (
 df.replace('', np.nan) # get rid of empty strings
   # reshape to long
   .melt(id_vars="Date", value_name='Items').dropna().reset_index(drop=True)
   # deduplicate
   .assign(n=lambda d: d.groupby(['Date', 'Items']).cumcount().add(1))
   .pivot(index="Date", columns=['Items', 'n'], values='variable')
   # flatten the MultiIndex
   .pipe(lambda d: d.set_axis(d.columns.map(lambda x: f'{x[0]}_{x[1]}'), axis=1))
   # fill NaN with empty strings and reset index
   .fillna('').reset_index()
)

print(out)

    Output:

            Date Floors_1 Roof_1 Paint_1 Tables_1 Roof_2 Paint_2
0  4/04/2023      Jim     Ed   James      Bob            Joe
1  4/05/2023      Bob    Jim     Joe       Ed  James        
2  4/06/2023       Ed    Joe     Jim    James               
3  4/07/2023    James    Jim     Bob      Joe