For loop and Conditionals in pandas DataFrame

Question

I have this DataFrame and I need to write a conditionals to extract only the starred Energy.

Energy  Time
0       80
0       82 
0       84
0       86
287**   88
287     90
287     91
287     92
0       94
0       96
0       98
302**   100
302     102
302     104
302     106
0       108
0       110

The idea is to accepts Energy values when Energy(t)>0 & Energy(t-1)==0.

I tried creating a for loop

set_time=set(df.loc[:,'Time'])
list_time=list(set_time)
for t, time in enumerate(list_time):
     if df['Energy'][t] > 0 & df['Energy'][t-1]==0:
        print(df['Energy'],t)

But I get errors. Thanks a lot in advance

What errors do you get?

Ray
– Ray

2018-02-22 20:33:37 +00:00
Commented Feb 22, 2018 at 20:33 — Ray
– Ray, Commented Feb 22, 2018 at 20:33
KeyError: 'Energy'

Annalix
– Annalix

2018-02-23 09:58:55 +00:00
Commented Feb 23, 2018 at 9:58 — Annalix
– Annalix, Commented Feb 23, 2018 at 9:58

BENY · Accepted Answer · 2018-02-22 18:02:26Z

1

There is one way

v=df.eq(0).Energy.cumsum()

df.groupby(df.eq(0).Energy.cumsum()).head(2).loc[df.groupby(v).Energy.filter(lambda x : x.ne(0).any()).index].dropna()

Out[1538]: 
    Energy   Time
3      0.0   86.0
4    287.0   88.0
10     0.0   98.0
11   302.0  100.0

answered Feb 22, 2018 at 18:02

BENY

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2 Comments

Annalix Over a year ago

Thanks Wen, pls could you explain a little bit what did you do? what is eq(0) cumsum()...?

BENY Over a year ago

@Annalix cumsum :pandas.pydata.org/pandas-docs/stable/generated/…, eq == '='

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