Datetime index filtering and changing of values

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Date COL_1 COL_2
2017-04-21 0.0 NaN
2017-04-24 1.0 0.0
2017-04-25 0.0 -1.0

Have the following table in datetime index.

What's the best way do I put in a conditional statement to filter where if COL_1 of the earliest index date is 0, COL_2 of the earliest index date, (Nan), is set to -1.

Need to keep it dynamic and filter without mentioning the specific dates.

Thanks!

pandas python-3.x datetime
1 Answers

IIUC:

df.loc[(df.index == df.index.min()) & (df['COL_1'] == 0), 'COL_2'] = -1
print(df)

# Output
            COL_1  COL_2
2017-04-21    0.0   -1.0
2017-04-24    1.0    0.0
2017-04-25    0.0   -1.0
user_152399510
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