For example, I have a dataframe:
cond value1 value2
0 True 1 1
1 False 3 5
2 True 34 2
3 True 23 23
4 False 4 2
I hope to replace value1 to value2*2 when cond=True. So I want the result is:
cond value1 value2
0 True 2 1
1 False 3 5
2 True 4 2
3 True 46 23
4 False 4 2
I can achieve it by follow code:
def convert(x):
if x.cond:
x.value1= x.value2*2
return x
data = data.apply(lambda x: convert(x),axis=1)
I think it is so slow when data is big. I try it by .loc, but I don't know how to set value.
How can I achieve it by .loc or other simple ways? Thanks in advance.
Create boolean mask and multiple only filtered rows:
mask = df.cond
df.loc[mask, 'value1'] = df.loc[mask, 'value2'] * 2
print (df)
cond value1 value2
0 True 2 1
1 False 3 5
2 True 4 2
3 True 46 23
4 False 4 2
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