Python 如何替换 Pandas.DataFrame 上的整列
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how to replace an entire column on Pandas.DataFrame
提问by Stefano Fedele
I would like to replace an entire column on a Pandas DataFrame with another column taken from another DataFrame, an example will clarify what I am looking for
我想用从另一个 DataFrame 中获取的另一列替换 Pandas DataFrame 上的整个列，一个示例将阐明我正在寻找的内容
import pandas as pd
dic = {'A': [1, 4, 1, 4], 'B': [9, 2, 5, 3], 'C': [0, 0, 5, 3]}
df = pd.DataFrame(dic)
df is
df 是
'A' 'B' 'C'
1 9 0
4 2 0
1 5 5
4 3 3
Now I have another dataframe called df1 with a column "E" that is
现在我有另一个名为 df1 的数据框，其中有一列“E”
df1['E'] = [ 4, 4, 4, 0]
and I would like to replace column "B" of df with column "E" of df1
我想用df1的“E”列替换df的“B”列
'A' 'E' 'C'
1 4 0
4 4 0
1 4 5
4 0 3
I tried to use the .replace() method in many ways but I didn't get anything good. Can you help me?
我尝试以多种方式使用 .replace() 方法，但没有得到任何好处。你能帮助我吗？
采纳答案by Jamie Edgecombe
If you don't mind getting a new data frame object returned as opposed to updating the original Pandas .assign()will avoid SettingWithCopyWarning. Your example:
如果您不介意返回一个新的数据框对象而不是更新原始Pandas，那么 .assign()将避免SettingWithCopyWarning. 你的例子：
df = df.assign(B=df1['E'])
回答by EdChum
If the indices match then:
如果索引匹配，则：
df['B'] = df1['E']
should work otherwise:
否则应该工作：
df['B'] = df1['E'].values
will work so long as the length of the elements matches
只要元素的长度匹配就可以工作
回答by Chege
For those that struggle with the "SettingWithCopy" warning, here's a workaround which may not be so efficient, but still gets the job done.
对于那些因“SettingWithCopy”警告而苦恼的人，这里有一个可能效率不高但仍能完成工作的解决方法。
Suppose you with to overwrite column_1 and column_3, but retain column_2 and column_4
假设您覆盖 column_1 和 column_3，但保留 column_2 和 column_4
columns_to_overwrite = ["column_1", "column_3"]
First delete the columns that you intend to replace...
首先删除要替换的列...
original_df.drop(labels=columns_to_overwrite, axis="columns", inplace=True)
... then re-insert the columns, but using the values that you intended to overwrite
...然后重新插入列，但使用您打算覆盖的值
original_df[columns_to_overwrite] = other_data_frame[columns_to_overwrite]
