ifelse statement in python similar to R

Question

Is there any ifelse statement in python similar to R? I have a pandas.core.series.Series ds of length 64843. I need to take log of each data point of this series. Some of the value in series are 0. In R I could write

ifelse(ds==0,0,log(z))

But in python I'm not seeing similar type of statement. Can you please guide me?

Possible duplicate of [Does Python have a ternary conditional operator?](https://stackoverflow.com/questions/394809/does-python-have-a-ternary-conditional-operator) — Christian König, Nov 26 '18 at 07:55
In python there's elif statement which I think is the equivalent is that what you're asking? — Alex Tănăsescu, Nov 26 '18 at 18:31

jezrael · Accepted Answer · 2018-11-26T08:04:17.917

2

I believe you need numpy.where generally, but for log is possible add parameter where to numpy.log.

This functions return numpy 1d array, so for new Series is necessary contructor:

s = pd.Series([0,1,5])

s1 = pd.Series(np.log(s,where=s>0), index=s.index)

Or:

s1 = pd.Series(np.where(s==0,0,np.log(s)), index=s.index)
print (s1)
0    0.000000
1    0.000000
2    1.609438
dtype: float64

edited Nov 26 '18 at 08:04

answered Nov 26 '18 at 07:59

jezrael

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score 0 · Answer 2 · answered Nov 26 '18 at 08:10

I think in your case it is easier to just fill in the 0's first and then call log:

ds[ds == 0] = 1
ds = np.log(ds)

Be careful when you have values in your Series between 0 and 1, those will map to -Inf and 0, so your scale will not be continuous anymore.

score -1 · Answer 3 · answered Nov 26 '18 at 08:00

-1

Maybe

ds[0 if ds == 0 else math.log(ds)]

answered Nov 26 '18 at 08:00

Nick

1

From review: could you please add more detail to your answer? – toti08 Nov 26 '18 at 08:11

ifelse statement in python similar to R

3 Answers3