Pandas: IF value in dataframe1...THEN decrease value in dataframe2

Question

is anyone familiar with if...conditions in pandas and can help me with a petite question for a beginner? right now I have this:

tmy_data.loc[tmy_data['elevation of sun'] <= 10, 'DNI'] = 0

But instead of setting the'DNI' to zero when 'elevation of sun' is less then 10, I want it to decrease to 80% Probably its not that complicated...but I still have no idea my try just ended in decreasing the whole dataframe instead of the single value

Answer 1

If you want to save to the existing column 'DNI'

tmy_data.loc[tmy_data['elevation of sun'] <= 10, 'DNI'] = tmy_data['DNI']*0.8

If you want to save to a new column 'DNI_new'

tmy_data.loc[tmy_data['elevation of sun'] <= 10, 'DNI_new'] = tmy_data['DNI']*0.8