python 中的 pandas 插入方法-ag捕鱼王app官网

本教程解释了如何使用 insert() 方法在 pandas dataframe 中插入一列。

import pandas as pd
countries_df = pd.dataframe(
    {
        "country": ["nepal", "switzerland", "germany", "canada"],
        "continent": ["asia", "europe", "europe", "north america"],
        "primary language": ["nepali", "french", "german", "english"],
    }
)
print("countries dataframe:")
print(countries_df, "\n")

输出：

countries dataframe:
       country      continent primary language
0        nepal           asia           nepali
1  switzerland         europe           french
2      germany         europe           german
3       canada  north america          english

我们将使用上例中所示的 countries_df dataframe 来解释如何使用 insert() 方法在 pandas dataframe 中插入一列。

pandas.dataframe.insert() 方法

语法

dataframe.insert(loc, column, value, allow_duplicates=false)

它将名为 column 的列插入到 dataframe 中，其值由 value 指定，位于 loc 位置。

使用 insert() 方法插入对所有行具有相同值的列

import pandas as pd
countries_df = pd.dataframe(
    {
        "country": ["nepal", "switzerland", "germany", "canada"],
        "continent": ["asia", "europe", "europe", "north america"],
        "primary language": ["nepali", "french", "german", "english"],
    }
)
print("countries dataframe:")
print(countries_df, "\n")
countries_df.insert(3, "capital", "unknown")
print("countries dataframe after inserting capital column:")
print(countries_df)

输出：

countries dataframe:
       country      continent primary language
0        nepal           asia           nepali
1  switzerland         europe           french
2      germany         europe           german
3       canada  north america          english
countries dataframe after inserting capital column:
       country      continent primary language  capital
0        nepal           asia           nepali  unknown
1  switzerland         europe           french  unknown
2      germany         europe           german  unknown
3       canada  north america          english  unknown

它在 countries_df dataframe 的 3 索引位置插入 ·capital·列，所有行的 ·capital·列值均设置为 unknown。

该位置从 0 开始，因此 3 位置指的是 dataframe 中的 4 列。

在 dataframe 中插入一列，指定每行的值

如果我们想使用 insert() 方法为要插入的列指定每一行的值，我们可以在 insert() 方法中传递一个值列表作为 value 参数。

import pandas as pd
countries_df = pd.dataframe(
    {
        "country": ["nepal", "switzerland", "germany", "canada"],
        "continent": ["asia", "europe", "europe", "north america"],
        "primary language": ["nepali", "french", "german", "english"],
    }
)
print("countries dataframe:")
print(countries_df, "\n")
capitals = ["kathmandu", "zurich", "berlin", "ottawa"]
countries_df.insert(2, "capital", capitals)
print("countries dataframe after inserting capital column:")
print(countries_df)

输出：

countries dataframe:
       country      continent primary language
0        nepal           asia           nepali
1  switzerland         europe           french
2      germany         europe           german
3       canada  north america          english
countries dataframe after inserting capital column:
       country      continent    capital primary language
0        nepal           asia  kathmandu           nepali
1  switzerland         europe     zurich           french
2      germany         europe     berlin           german
3       canada  north america     ottawa          english

它在 dataframe countries_df 中的索引 2 插入了列 capital，并为 dataframe 中的 capital 列指定了每一行的值。

在 insert() 方法中设置 allow_duplicates = true 来添加已经存在的列

import pandas as pd
countries_df = pd.dataframe(
    {
        "country": ["nepal", "switzerland", "germany", "canada"],
        "continent": ["asia", "europe", "europe", "north america"],
        "primary language": ["nepali", "french", "german", "english"],
        "capital": ["kathmandu", "zurich", "berlin", "ottawa"],
    }
)
print("countries dataframe:")
print(countries_df, "\n")
capitals = ["kathmandu", "zurich", "berlin", "ottawa"]
countries_df.insert(4, "capital", capitals, allow_duplicates=true)
print("countries dataframe after inserting capital column:")
print(countries_df)

输出：

countries dataframe:
       country      continent primary language    capital
0        nepal           asia           nepali  kathmandu
1  switzerland         europe           french     zurich
2      germany         europe           german     berlin
3       canada  north america          english     ottawa
countries dataframe after inserting capital column:
       country      continent primary language    capital    capital
0        nepal           asia           nepali  kathmandu  kathmandu
1  switzerland         europe           french     zurich     zurich
2      germany         europe           german     berlin     berlin
3       canada  north america          english     ottawa     ottawa

它将列 capital 添加到 countries_df dataframe 中，尽管 countries_df dataframe 中已经存在 capital 列。

如果我们尝试插入已经存在于 dataframe 中的列，而没有在 insert() 方法中设置 allow_duplicates = true，它就会向我们抛出一个错误信息：valueerror: cannot insert column, already exists.。