Unique values of two columns for pandas dataframe

Question

Suppose I have pandas data frame with 2 columns:

df: Col1  Col2
      1     1
      1     2
      1     2
      1     2
      3     4
      3     4

Then I want to keep only the unique couple values (col1, col2) of these two columns and give their frequncy:

df2: Col1  Col2  Freq
      1     1     1
      1     2     3
      3     4     2

I think to use df['Col1', 'Col2'].value_counts() but it works only for one column.
Does it exist a function to deal with many columns?

Asked By: curious_one

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Source

Answer 1

You could try

df.groupby(['Col1', 'Col2']).size()

for a different visual output in comparison to jez’s answer, you can extend that solution with

pd.DataFrame(df.groupby(['Col1', 'Col2']).size().rename('Freq'))

gives

           Freq
Col1 Col2      
1    1        1
     2        3
3    4        2

Answered By: Quickbeam2k1

Answer 2

You need groupby + size + Series.reset_index:

df = df.groupby(['Col1', 'Col2']).size().reset_index(name='Freq')
print (df)
   Col1  Col2  Freq
0     1     1     1
1     1     2     3
2     3     4     2

Answered By: jezrael

Unique values of two columns for pandas dataframe

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