pandas dataframe：如何计算初始年份的百分比变化（在时间 t）

Question

我有以下 dataframe (df)：

import numpy as np
import pandas as pd
import matplotlib.pyplot as plt
import seaborn as sns
import pickle
import matplotlib as mpl

sns.set()

df = pd.DataFrame({ 

    # some ways to create random data
    'scenario':np.random.choice( ['BAU','ETS','ESD'], 27),
    'region':np.random.choice( ['Italy','France'], 27),
    'variable':np.random.choice( ['GDP','GHG'], 27),
    # some ways to create systematic groups for indexing or groupby
    # this is similar to r's expand.grid(), see note 2 below
    '2015':np.random.randn(27),
    '2016':np.random.randn(27),
    '2017':np.random.randn(27),
    '2018':np.random.randn(27),
    '2019':np.random.randn(27),
    '2020':np.random.randn(27),
    '2021':np.random.randn(27)
    })

df2=pd.melt(df,id_vars=['scenario','region','variable'],var_name='year')
all_names_index = df2.set_index(['scenario','region','variable','year']).sort_index()

我如何计算每个变量、情景和区域相对于初始年份（即 2015 年）的百分比变化？

举个例子：

2016=(2016-2015)/2015
2017=(2017-2015)/2015
...
2021=(2021-2015)/2015

Answer 1

您可以尝试从每个组中减去第一个元素，我将同一年的值相加：

all_names_index.reset_index(inplace=True)
all_names_index = all_names_index.groupby(by=['scenario', 'region', 'variable', 'year']).sum().reset_index()
all_names_index['pct_change'] = all_names_index.groupby(by=['scenario', 'region', 'variable'])['value'].apply(lambda x: x.div(x.iloc[0]).subtract(1).mul(100))
print(all_names_index)

Output：

   scenario  region variable  year     value  pct_change
0       BAU  France      GDP  2015  1.786506    0.000000
1       BAU  France      GDP  2016  0.020103  -98.874740
2       BAU  France      GDP  2017  3.190068   78.564690
3       BAU  France      GDP  2018 -3.581261 -300.461753
4       BAU  France      GDP  2019  0.500374  -71.991488
..      ...     ...      ...   ...       ...         ...
72      ETS   Italy      GDP  2017 -0.557029 -153.990905
73      ETS   Italy      GDP  2018 -0.172391 -116.709261
74      ETS   Italy      GDP  2019 -0.238212 -123.089063
75      ETS   Italy      GDP  2020 -1.098866 -206.509438
76      ETS   Italy      GDP  2021 -0.405364 -139.290556