CODEWITHSUNDEEP
pythonpandasdataframe
CarterB
CarterB

Reputation: 542

Setting value of row in certain column based on a slice of pandas dataframe - using both loc and iloc

I am trying to slice my dataframe based on a certain condition, and select the first row of that slice, and set the value of the column of that first row.

index  COL_A. COL.B. COLC
0.     cond_A1 cond_B1.  0
1      cond_A1 cond_B1.  0
2      cond_A1 cond_B1.  0
3      cond_A2 cond_B2.  0
4.     cond_A2 cond_B2.  0

Neither of the following lines of code I have attempted update the dataframe

df.loc[((df['COL_A'] == cond_A1) & (df['COL_B'] == cond_b1)), 'COL_C'].iloc[0] = 1
df[((df['COL_A'] == cond_A1) & (df['COL_B'] == cond_b1))].iloc[0]['COL_C'] = 1

I need to be able to loop through the conditions so that I could apply the same code to the next set of conditions, and update the COL_C row with index 3 based on these new conditions.

Upvotes: 0

Views: 34

Answers (1)

IoaTzimas
IoaTzimas

Reputation: 10624

You can update only the first row of your slice with the following code:

df.loc[df.loc[(df['COL_A'] == cond_A1) & (df['COL_B'] == cond_b1), 'COL_C'].index[0], 'COL_C'] = 1

Upvotes: 1

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