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pythonpandas
Simon Yeung
Simon Yeung

Reputation: 3

Python Pandas: Changing a Value base on index

For example, I have the following data frame df

     r1     r2  
1    False  10  
2    True   20  
3    True   40

I would like to change the value of r2 to become the value of its index to the power of its index if r1 is True

pow(index, index)

The desired result is

      r1     r2  
1    False  10  
2    True   4  
3    True   27

I know how to target the cells which the values need to be changed, but I just know how to set them to a constant i.e. 0

df.loc[df['r1'] == True, 'r2'] = 0

But I don't know how to set it to a function of its index

Thank you for the help

Upvotes: 0

Views: 61

Answers (2)

piRSquared
piRSquared

Reputation: 294516

Using pd.DataFrame.mask 

df.r2.mask(df.r1, df.index ** df.index, inplace=True)
df

      r1  r2
1  False  10
2   True   4
3   True  27

Upvotes: 2

cs95
cs95

Reputation: 403130

Use df.r1 to find the index, then index r2 and reassign.

idx = df[df['r1']].index     
df.loc[df['r1'], 'r2'] = idx ** idx

print(df)
      r1  r2
1  False  10
2   True   4
3   True  27

Upvotes: 1

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