如何在pyspark中将2列汇总到地图中

我有一个这样的DataFrame

a = spark.createDataFrame([['Alice', '2020-03-03', '1'], ['Bob', '2020-03-03', '1'], ['Bob', '2020-03-05', '2']], ['name', 'dt', 'hits'])
a.show()
+-----+----------+----+
| name|        dt|hits|
+-----+----------+----+
|Alice|2020-03-03|   1|
|  Bob|2020-03-03|   1|
|  Bob|2020-03-05|   2|
+-----+----------+----+

我想将dt汇总并点击Columns进入地图-

+-----+------------------------------------+
| name|    map                             |
+-----+------------------------------------+
|Alice|   {'2020-03-03': 1, '2020-03-05':2}|
|  Bob|   {'2020-03-03': 1}                |
+-----+------------------------------------+

但是此代码引发异常:

from pyspark.sql import functions as F
a = a.groupBy(F.col('name')).agg(F.create_map(F.col('dt'), F.col('hits')))

Py4JJavaError: An error occurred while calling o2920.agg.
: org.apache.spark.sql.AnalysisException: expression '`dt`' is neither present in the group by, nor is it an aggregate function. Add to group by or wrap in first() (or first_value) if you don't care which value you get.;;
Aggregate [name#1329], [name#1329, map(dt#1330, hits#1331) AS map(dt, hits)#1361]
+- LogicalRDD [name#1329, dt#1330, hits#1331], false

我究竟做错了什么?