多指数组由 pandas 数据帧 [英] MultiIndex Group By in Pandas Data Frame
问题描述
我有一个数据集,包含按国家统计的经济指标的年份,如下所示:
I have a data set that contains countries and statistics on economic indicators by year, organized like so:
Country Metric 2011 2012 2013 2014
USA GDP 7 4 0 2
USA Pop. 2 3 0 3
GB GDP 8 7 0 7
GB Pop. 2 6 0 0
FR GDP 5 0 0 1
FR Pop. 1 1 0 5
如何在熊猫中使用MultiIndex创建仅显示GDP的数据框架每个国家的年份?
How can I use MultiIndex in pandas to create a data frame that only shows GDP by Year for each country?
我试过:
df = data.groupby(['Country', 'Metric'])
但它没有正常工作。
推荐答案
在这种情况下,实际上并不需要 groupby
。您也没有 MultiIndex
。您可以这样做:
In this case, you don't actually need a groupby
. You also don't have a MultiIndex
. You can make one like this:
import pandas
from io import StringIO
datastring = StringIO("""\
Country Metric 2011 2012 2013 2014
USA GDP 7 4 0 2
USA Pop. 2 3 0 3
GB GDP 8 7 0 7
GB Pop. 2 6 0 0
FR GDP 5 0 0 1
FR Pop. 1 1 0 5
""")
data = pandas.read_table(datastring, sep='\s\s+')
data.set_index(['Country', 'Metric'], inplace=True)
然后数据
如下所示:
2011 2012 2013 2014
Country Metric
USA GDP 7 4 0 2
Pop. 2 3 0 3
GB GDP 8 7 0 7
Pop. 2 6 0 0
FR GDP 5 0 0 1
Pop. 1 1 0 5
现在要获得GDP,您可以通过数据框的横截面 xs
方法:
Now to get the GDPs, you can take a cross-section of the dataframe via the xs
method:
data.xs('GDP', level='Metric')
2011 2012 2013 2014
Country
USA 7 4 0 2
GB 8 7 0 7
FR 5 0 0 1
这很简单,因为你的数据已经被摆放/解除了。如果他们没有,看起来像这样:
It's so easy because your data are already pivoted/unstacked. IF they weren't and looked like this:
data.columns.names = ['Year']
data = data.stack()
data
Country Metric Year
USA GDP 2011 7
2012 4
2013 0
2014 2
Pop. 2011 2
2012 3
2013 0
2014 3
GB GDP 2011 8
2012 7
2013 0
2014 7
Pop. 2011 2
2012 6
2013 0
2014 0
FR GDP 2011 5
2012 0
2013 0
2014 1
Pop. 2011 1
2012 1
2013 0
2014 5
你然后可以使用 groupby
来告诉你整个世界:
You could then use groupby
to tell you something about the world as a whole:
data.groupby(level=['Metric', 'Year']).sum()
Metric Year
GDP 2011 20
2012 11
2013 0
2014 10
Pop. 2011 5
2012 10
2013 0
2014 8
或得到真正的幻想:
data.groupby(level=['Metric', 'Year']).sum().unstack(level='Metric')
Metric GDP Pop.
Year
2011 20 5
2012 11 10
2013 0 0
2014 10 8
这篇关于多指数组由 pandas 数据帧的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!