pandas - How to pick a season/month over several years from a pandas dataframe?
问题描述
I've got a pandas dataframe with data over three consecutive years... Is there an easy way to pick the summer/winter periods?
At the moment, I do this:
df_summer = df[((df.index.month > 5) & (df.index.month < 9))]
df_winter = df[((df.index.month < 3) | (df.index.month == 12))]
but from xarray I'm used to a notation like:
xa_summer = xa[xa.dt.season=='JJA']
for one year I could do:
df_summer = df['YYYYMMDDHH':'YYYYMMDDHH']
Is there a more intuitive way to pick a season over multiple years in pandas?
Thanks...
解决方案
它还没有在pandas中实现。
一个想法是season
通过模数 by 12
, add 3
, floor 除以3
和 last map
by 字典创建助手:
rng = pd.date_range('2017-04-03', periods=40, freq='MS')
df = pd.DataFrame({'a': range(40)}, index=rng)
#print (df)
season = ((df.index.month % 12 + 3) // 3).map({1:'DJF', 2: 'MAM', 3:'JJA', 4:'SON'})
print (season)
Index(['MAM', 'JJA', 'JJA', 'JJA', 'SON', 'SON', 'SON', 'DJF', 'DJF', 'DJF',
'MAM', 'MAM', 'MAM', 'JJA', 'JJA', 'JJA', 'SON', 'SON', 'SON', 'DJF',
'DJF', 'DJF', 'MAM', 'MAM', 'MAM', 'JJA', 'JJA', 'JJA', 'SON', 'SON',
'SON', 'DJF', 'DJF', 'DJF', 'MAM', 'MAM', 'MAM', 'JJA', 'JJA', 'JJA'],
dtype='object')
df_summer = df[season == 'JJA']
print (df_summer)
a
2017-06-01 1
2017-07-01 2
2017-08-01 3
2018-06-01 13
2018-07-01 14
2018-08-01 15
2019-06-01 25
2019-07-01 26
2019-08-01 27
2020-06-01 37
2020-07-01 38
2020-08-01 39
df_winter = df[season == 'DJF']
print (df_winter)
a
2017-12-01 7
2018-01-01 8
2018-02-01 9
2018-12-01 19
2019-01-01 20
2019-02-01 21
2019-12-01 31
2020-01-01 32
2020-02-01 33
或创建新列:
df_summer = df[df['season'] == 'JJA']
print (df_summer)
a season
2017-06-01 1 JJA
2017-07-01 2 JJA
2017-08-01 3 JJA
2018-06-01 13 JJA
2018-07-01 14 JJA
2018-08-01 15 JJA
2019-06-01 25 JJA
2019-07-01 26 JJA
2019-08-01 27 JJA
2020-06-01 37 JJA
2020-07-01 38 JJA
2020-08-01 39 JJA
df_winter = df[df['season'] == 'DJF']
print (df_winter)
a season
2017-12-01 7 DJF
2018-01-01 8 DJF
2018-02-01 9 DJF
2018-12-01 19 DJF
2019-01-01 20 DJF
2019-02-01 21 DJF
2019-12-01 31 DJF
2020-01-01 32 DJF
2020-02-01 33 DJF
另一个想法是按月使用Index.isin
:
df_summer = df[df.index.month.isin([6,7,8])]
print (df_summer)
a
2017-06-01 1
2017-07-01 2
2017-08-01 3
2018-06-01 13
2018-07-01 14
2018-08-01 15
2019-06-01 25
2019-07-01 26
2019-08-01 27
2020-06-01 37
2020-07-01 38
2020-08-01 39
df_winter = df[df.index.month.isin([12,1,2])]
print (df_winter)
a
2017-12-01 7
2018-01-01 8
2018-02-01 9
2018-12-01 19
2019-01-01 20
2019-02-01 21
2019-12-01 31
2020-01-01 32
2020-02-01 33
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