Pandas Dataframe:如何在其他列中添加具有出现次数的列 [英] Pandas Dataframe: how to add column with number of occurrences in other column

问题描述

我必须遵循df:

Col1    Col2
test    Something
test2   Something
test3   Something
test    Something
test2   Something
test5   Something

我想得到

Col1    Col2          Occur
test    Something     2
test2   Something     2
test3   Something     1
test    Something     2
test2   Something     2
test5   Something     1

我尝试使用:

df["Occur"] = df["Col1"].value_counts()

但这没有帮助.我的Occur栏充满了"NaN"

But it didn't help. I've got Occur column full of 'NaN'

推荐答案

groupby ，然后应用Col2上的> transform 返回其索引与原始df对齐的Series，因此您可以将其添加为列:

groupby on 'col1' and then apply transform on Col2 to return a Series with its index aligned to the original df so you can add it as a column:

In [3]:
df['Occur'] = df.groupby('Col1')['Col2'].transform(pd.Series.value_counts)
df

Out[3]:
    Col1       Col2 Occur
0   test  Something     2
1  test2  Something     2
2  test3  Something     1
3   test  Something     2
4  test2  Something     2
5  test5  Something     1

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