如何在Spark SQL中对多个列进行透视? [英] How to pivot on multiple columns in Spark SQL?
问题描述
我需要在pyspark数据框中旋转多个列.样本数据框，
I need to pivot more than one column in a pyspark dataframe. Sample dataframe,
>>> d = [(100,1,23,10),(100,2,45,11),(100,3,67,12),(100,4,78,13),(101,1,23,10),(101,2,45,13),(101,3,67,14),(101,4,78,15),(102,1,23,10),(102,2,45,11),(102,3,67,16),(102,4,78,18)]
>>> mydf = spark.createDataFrame(d,['id','day','price','units'])
>>> mydf.show()
+---+---+-----+-----+
| id|day|price|units|
+---+---+-----+-----+
|100| 1| 23| 10|
|100| 2| 45| 11|
|100| 3| 67| 12|
|100| 4| 78| 13|
|101| 1| 23| 10|
|101| 2| 45| 13|
|101| 3| 67| 14|
|101| 4| 78| 15|
|102| 1| 23| 10|
|102| 2| 45| 11|
|102| 3| 67| 16|
|102| 4| 78| 18|
+---+---+-----+-----+
现在，如果我需要根据天将每个ID的价格列划分为一行，则可以使用数据透视方法，
Now,if I need to get price column into a row for each id based on day, then I can use pivot method as,
>>> pvtdf = mydf.withColumn('combcol',F.concat(F.lit('price_'),mydf['day'])).groupby('id').pivot('combcol').agg(F.first('price'))
>>> pvtdf.show()
+---+-------+-------+-------+-------+
| id|price_1|price_2|price_3|price_4|
+---+-------+-------+-------+-------+
|100| 23| 45| 67| 78|
|101| 23| 45| 67| 78|
|102| 23| 45| 67| 78|
+---+-------+-------+-------+-------+
所以当我需要单位列也要作为价格转置时，我要么像上面一样为单位再创建一个数据框，然后使用id将它们都加入.但是，当我有更多这样的列时，我尝试了一个函数为此，
so when I need units column as well to be transposed as price, either I got to create one more dataframe as above for units and then join both using id.But, when I have more columns as such, I tried a function to do it,
>>> def pivot_udf(df,*cols):
... mydf = df.select('id').drop_duplicates()
... for c in cols:
... mydf = mydf.join(df.withColumn('combcol',F.concat(F.lit('{}_'.format(c)),df['day'])).groupby('id').pivot('combcol').agg(F.first(c)),'id')
... return mydf
...
>>> pivot_udf(mydf,'price','units').show()
+---+-------+-------+-------+-------+-------+-------+-------+-------+
| id|price_1|price_2|price_3|price_4|units_1|units_2|units_3|units_4|
+---+-------+-------+-------+-------+-------+-------+-------+-------+
|100| 23| 45| 67| 78| 10| 11| 12| 13|
|101| 23| 45| 67| 78| 10| 13| 14| 15|
|102| 23| 45| 67| 78| 10| 11| 16| 18|
+---+-------+-------+-------+-------+-------+-------+-------+-------+
需要这样做的建议，如果这样做是一种好的做法，以及是否有其他更好的做法.预先感谢！
Need suggestions on ,if it is good practice to do so and if any other better way of doing it. Thanks in advance!
推荐答案
这是涉及单个枢轴的非UDF方法(因此，只需一次列扫描即可识别所有唯一日期).
Here's a non-UDF way involving a single pivot (hence, just a single column scan to identify all the unique dates).
dff = mydf.groupBy('id').pivot('day').agg(F.first('price').alias('price'),F.first('units').alias('unit'))
这是结果(对不匹配的排序和命名表示歉意):
Here's the result (apologies for the non-matching ordering and naming):
+---+-------+------+-------+------+-------+------+-------+------+
| id|1_price|1_unit|2_price|2_unit|3_price|3_unit|4_price|4_unit|
+---+-------+------+-------+------+-------+------+-------+------+
|100| 23| 10| 45| 11| 67| 12| 78| 13|
|101| 23| 10| 45| 13| 67| 14| 78| 15|
|102| 23| 10| 45| 11| 67| 16| 78| 18|
+---+-------+------+-------+------+-------+------+-------+------+
我们只需要在当天进行数据透视后在price和unit列上进行汇总即可.
We just aggregate both on the price and the unit column after pivoting on the day.
如果需要命名，
dff.select([F.col(c).name('_'.join(x for x in c.split('_')[::-1])) for c in dff.columns]).show()
+---+-------+------+-------+------+-------+------+-------+------+
| id|price_1|unit_1|price_2|unit_2|price_3|unit_3|price_4|unit_4|
+---+-------+------+-------+------+-------+------+-------+------+
|100| 23| 10| 45| 11| 67| 12| 78| 13|
|101| 23| 10| 45| 13| 67| 14| 78| 15|
|102| 23| 10| 45| 11| 67| 16| 78| 18|
+---+-------+------+-------+------+-------+------+-------+------+
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