Percantage change in python dataframe based on index

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I have a dataframe in Python. I am looking for a way to calculate percentage change of a column based on the value of the first column of the table.

  Number  |  Value
_____________________
    1          1
    1          1,5
    1          1,5
    1          3
    2          300
    2          200
    2          250
    2          350
   ...         ...

This is how I would like the dataframe to look:

  Number  |  Value  |  pct_change   
___________________________________
    1         1      
    1         1,5         0,5                 
    1         1,5         0,0    
    1         3           1,0
    2         300         
    2         200         -0,33
    2         250         0,25
    2         350         0,40
   ...        ...         ...
percentage dataframe python
1 Answers

Assuming pandas, you can apply pct_change per group:

df['pct_change'] = df.groupby('Number')['Value'].pct_change()

output:

   Number  Value  pct_change
0       1    1.0         NaN
1       1    1.5    0.500000
2       1    1.5    0.000000
3       1    3.0    1.000000
4       2  300.0         NaN
5       2  200.0   -0.333333
6       2  250.0    0.250000
7       2  350.0    0.400000

NB. ensure that you have numeric values. The decimal separator in python is a dot .. To convert from strings with commas, use: df['Value'] = pd.to_numeric(df['Value'].str.replace(',', '.', regex=False))

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