根据另一列的值从一列复制值 [英] Copy value from one column based on the value of another column

问题描述

我正在尝试根据第四列中的值填充其他两列中的一列中的值.

I'm trying to fill values in one column from two other columns based on the values in a fourth column.

我有一个包含四列的 Pandas 数据框:A、B、C、D

I have a pandas dataframe with four columns: A, B, C, D

df_copy = df.copy()
for i, row in df.iterrows():
    if 'Test' in row.D:
        df_copy.loc[i, 'A'] = row.B
    elif 'Other' in row.D:
        df_copy.loc[i, 'A'] = row.C

这行得通，但速度很慢.有没有更有效的方法?

This works, but is very slow. Is there a more efficient way?

推荐答案

您可以为此使用 'boolean indexing' 而不是迭代所有行:

You can use 'boolean indexing' for this instead of iterating over all rows:

df_copy.loc[df['D']=='Test', 'A'] = df['B']
df_copy.loc[df['D']=='Other', 'A'] = df['C']

如果你知道 D 列只包含这两个值，它甚至可以更短:

If you know that column D only consists of these two values, it can even shorter:

df_copy['A'] = df['B']
df_copy.loc[df['D']=='Other', 'A'] = df['C']

如果你想用与 in 一样的操作符来测试那个子串是否在列中，你可以这样做:

If you want to have the same as the in operator to test if that substring is in the column, you can do:

df['D'].str.contains('Other')

成为布尔值而不是 df['D']=='Other'

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