为什么PySpark中的agg（）一次只能汇总一列？

Question

对于下面的数据帧

df=spark.createDataFrame(data=[('Alice',4.300),('Bob',7.677)],schema=['name','High'])

当我试图找到最小值和最大值时，我只得到输出中的最小值。

df.agg({'High':'max','High':'min'}).show()

+-----------+
|min(High)  |
+-----------+
|    2094900|
+-----------+

为什么agg（）不能像熊猫那样同时给出max&min？

Answer 1

如您所见here：

agg(*exprs)

Compute aggregates and returns the result as a DataFrame.

The available aggregate functions are avg, max, min, sum, count.

If exprs is a single dict mapping from string to string, then the key is the column to perform aggregation on, and the value is the aggregate function.

Alternatively, exprs can also be a list of aggregate Column expressions.

Parameters: exprs – a dict mapping from column name (string) to aggregate functions (string), or a list of Column.

您可以使用列列表并对每列应用所需的函数，如下所示：

>>> from pyspark.sql import functions as F

>>> df.agg(F.min(df.High),F.max(df.High),F.avg(df.High),F.sum(df.High)).show()
+---------+---------+---------+---------+
|min(High)|max(High)|avg(High)|sum(High)|
+---------+---------+---------+---------+
|      4.3|    7.677|   5.9885|   11.977|
+---------+---------+---------+---------+