Transposing A Column In A Pandas Dataframe While Keeping Other Column Intact With Duplicates

My data frame is as follows selection_id last_traded_price 430494 1.46 430494 1.48 430494 1.56 430494 1.57 430495 2.45 430495 2.67 430495

Solution 1:

Option 1
groupby + apply

v = df.groupby('selection_id').last_traded_price.apply(list)
pd.DataFrame(v.tolist(), index=v.index)

                 0     1     2     3
selection_id                        
430494        1.46  1.48  1.56  1.57
430495        2.45  2.67  2.72  2.87

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Option 2
You can do this with pivot, as long as you have another column of counts to pass for the pivoting (it needs to be pivoted along something, that's why).

df['Count'] = df.groupby('selection_id').cumcount()
df.pivot('selection_id', 'Count', 'last_traded_price')

Count            0     1     2     3
selection_id                        
430494        1.46  1.48  1.56  1.57
430495        2.45  2.67  2.72  2.87

Solution 2:

You can use cumcount for Counter for new columns names created by set_index + unstack or pandas.pivot:

g = df.groupby('selection_id').cumcount()
df = df.set_index(['selection_id',g])['last_traded_price'].unstack()
print (df)
                 0     1     2     3
selection_id                        
430494        1.46  1.48  1.56  1.57
430495        2.45  2.67  2.72  2.87

Similar solution with pivot:

df = pd.pivot(index=df['selection_id'], 
              columns=df.groupby('selection_id').cumcount(), 
              values=df['last_traded_price'])
print (df)
                 0     1     2     3
selection_id                        
430494        1.46  1.48  1.56  1.57
430495        2.45  2.67  2.72  2.87