countDistinct 和 distinct.count 的区别 [英] The difference between countDistinct and distinct.count

问题描述

为什么 ..agg(countDistinct("member_id") as "count") 和 ..distinct.count 的输出不同?select count(distinct member_id)和select distinct count(member_id)的区别是一样的吗?

Why do I get different outputs for ..agg(countDistinct("member_id") as "count") and ..distinct.count? Is the difference the same as between select count(distinct member_id) and select distinct count(member_id)?

推荐答案

df.agg(countDistinct("member_id") as "count")

返回 member_id 列的不同值的数量，忽略所有其他列，而

returns the number of distinct values of the member_id column, ignoring all other columns, while

df.distinct.count

将计算 DataFrame 中不同记录的数量 - 其中distinct"表示所有列的值相同.

will count the number of distinct records in the DataFrame - where "distinct" means identical in values of all columns.

例如，DataFrame:

So, for example, the DataFrame:

+-----------+---------+
|member_name|member_id|
+-----------+---------+
|          a|        1|
|          b|        1|
|          b|        1|
+-----------+---------+

只有一个不同的 member_id 值但有两个不同的记录，因此 agg 选项将返回 1，而后者将返回 2.

has only one distinct member_id value but two distinct records, so the agg option would return 1 while the latter would return 2.

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