如何从DataFramePandas对象中选择特定列？

Question

我使用Quandlpython模块的get()函数从Quandl下载了一个时间序列，它的形状是(24,19)，但我只想使用第1到3列和第18列。我编写了这个脚本来完成这项工作，使用了一个名为ll的列表，并在我的DataFrame对象中应用了drop()方法，该列表包含了我不使用的列的名称。这里的挑战是不用创建列表就可以完成。

import Quandl
import pandas as pd

UNES_HARD_COAL_BR = Quandl.get("UENG/CL_BRA", authtoken="xX6ntNSFuvq7eCZvDdvL")
UNES_HARD_COAL_BR.columns = UNES_HARD_COAL_BR.columns.str.replace(' ', '_')



ll =['Hard_coal_-_transformation_(Metric_tons,_thousand)', 'Hard_coal_-_transformation_in_coke_ovens_(Metric_tons,_thousand)','Hard_coal_-_transformation_in_electricity,_CHP_and_heat_plants_(Metric_tons,_thousand)','Hard_coal_-_transformation_in_electricity_plants_-_main_activity_producers_(Metric_tons,_thousand)','Hard_coal_-_final_energy_consumption_(Metric_tons,_thousand)','Hard_coal_-_consumption_by_manufacturing,_construction_and_non-fuel_mining_industry_(Metric_tons,_thousand)','Hard_coal_-_consumption_by_other_manuf.,_const._and_non-fuel_ind._(Metric_tons,_thousand)','Hard_coal_-_final_consumption_(Metric_tons,_thousand)','Hard_coal_-_stock_changes_(Metric_tons,_thousand)','Hard_coal_-_transformation_in_electricity_plants_-_autoproducers_(Metric_tons,_thousand)','Hard_coal_-_consumption_by_transport_(Metric_tons,_thousand)','Hard_coal_-_consumption_by_rail_(Metric_tons,_thousand)','Hrad_coal_-_consumption_by_iron_and_steel_industry_(Metric_tons,_thousand)', 'Hard_coal_-_losses_(Metric_tons,_thousand)', 'Hard_coal_-_total_energy_supply_(Metric_tons,_thousand)']

UNES_HARD_COAL_BR.drop(ll, axis=1, inplace=True)

相关

How to select only specific columns from a DataFrame with MultiIndex columns?

pandas: Extracting specific selected columns from a DataFrame to new DataFrame

Answer 1

使用.iloc[]并注意pandas从0开始计算列数：

In [14]: UNES_HARD_COAL_BR = UNES_HARD_COAL_BR.iloc[:, [0,1,2,17]]

In [15]: UNES_HARD_COAL_BR.head()
Out[15]:
            Hard_coal_-_production_(Metric_tons,_thousand)  \
Date
1990-12-31                                          4595.0
1991-12-31                                          5188.0
1992-12-31                                          4731.0
1993-12-31                                          4595.0
1994-12-31                                          5134.0

            Hard_coal_-_imports_(Metric_tons,_thousand)  \
Date
1990-12-31                                      10146.0
1991-12-31                                      10758.0
1992-12-31                                      10399.0
1993-12-31                                      10975.0
1994-12-31                                      11319.0

            Hard_coal_-_exports_(Metric_tons,_thousand)  \
Date
1990-12-31                                          NaN
1991-12-31                                          NaN
1992-12-31                                          NaN
1993-12-31                                          NaN
1994-12-31                                          NaN

            Hard_coal_-_consumption_by_chemical_and_petrochemical_industry_(Metric_tons,_thousand)
Date
1990-12-31                                              260.0
1991-12-31                                              375.0
1992-12-31                                              390.0
1993-12-31                                              362.0
1994-12-31                                              354.0