[Pandas技巧] 添加新列

数据准备

import pandas as pd

df = pd.DataFrame([['ABC'],
                   ['FJZ'],
                   ['FOC']
                  ],columns=['Site'])

df

在平时开发中，添加新数据列涉及到以下三种常用方法:

1. 直接赋值

语法: df[新列名] = 值

import pandas as pd
import numpy as np

df = pd.DataFrame([['ABC'],
                   ['FJZ'],
                   ['FOC']
                  ],columns=['Site'])

# 添加空值数据列
# 添加'Level','Remark'列,将两列的值设置为空(keep blank)
df['Level'] = np.nan
df['Remark'] = np.nan

2.reindex()函数

语法: df.reindex(columns=[原来所有的列名,新增列名],fill_value=值)

import pandas as pd

df = pd.DataFrame([['ABC'],
                   ['FJZ'],
                   ['FOC']
                  ],columns=['Site'])

# 添加新列'Quantity'和'Product_number',并将其值设置为0
df = df.reindex(columns = ['Site', 'Quantity', 'Product_number'], fill_value=0)

注意: 不加fill_value参数，默认值为nan

3.loc()函数

语法: df.loc[:,新列名] = 值

import pandas as pd

df = pd.DataFrame([['ABC'],
                   ['FJZ'],
                   ['FOC']
                  ],columns=['Site'])

# 添加新列'Description',并将其值设置为'Good'
df.loc[:,'Description'] = 'Good'