Python 中的 Pandas 插入方法
Suraj Joshi
2023年1月30日
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.。
作者： Suraj Joshi
Suraj Joshi is a backend software engineer at Matrice.ai.
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