根据条目对数据框中的值进行计数 [英] Count values in dataframe based on entry

问题描述

我有一个数据框，其格式为:

I have a dataframe of the form:

category | value |
cat a    |x      |
cat a    |x      |
cat a    |y      |
cat b    |w      |
cat b    |z      |

我希望能够返回类似的信息(显示唯一的值和频率)

I'd like to be able to return something like (showing unique values and frequency)

category | freq of most common value |most common value |
cat a       2                              x
cat b       1                              w #(it doesnt matter if here is an w or z)

推荐答案

使用 Series.head :

df = (df.groupby('category', sort=False)['value']
        .apply(lambda x: x.value_counts().head(1))
        .reset_index()
        .rename(columns={'level_1':'most_common_value','value':'freq of most common value'}))
print (df)
  category most_common_value  freq of most common value
0    cat a                 x                          2
1    cat b                 w                          1

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