在Spark中获取组的最后一个值 [英] Getting last value of group in Spark
问题描述
我有一个SparkR DataFrame,如下所示:
I have a SparkR DataFrame as shown below:
#Create R data.frame
custId <- c(rep(1001, 5), rep(1002, 3), 1003)
date <- c('2013-08-01','2014-01-01','2014-02-01','2014-03-01','2014-04-01','2014-02-01','2014-03-01','2014-04-01','2014-04-01')
desc <- c('New','New','Good','New', 'Bad','New','Good','Good','New')
newcust <- c(1,1,0,1,0,1,0,0,1)
df <- data.frame(custId, date, desc, newcust)
#Create SparkR DataFrame
df <- createDataFrame(df)
display(df)
custId| date | desc | newcust
--------------------------------------
1001 | 2013-08-01| New | 1
1001 | 2014-01-01| New | 1
1001 | 2014-02-01| Good | 0
1001 | 2014-03-01| New | 1
1001 | 2014-04-01| Bad | 0
1002 | 2014-02-01| New | 1
1002 | 2014-03-01| Good | 0
1002 | 2014-04-01| Good | 0
1003 | 2014-04-01| New | 1
newcust
表示每次出现新的custId
时,或者同一custId
的desc
恢复为新"时,都有新客户.我要获取的是每个newcust
分组的最后一个desc
值,同时保持每个分组的第一个date
.以下是我要获取的DataFrame.如何在Spark中执行此操作? PySpark或SparkR代码均可使用.
newcust
indicates a new customer every time a new custId
appears, or if the same custId
's desc
reverts to 'New'. What I want to obtain is the last desc
value for each grouping of newcust
, while maintaining the first date
for each grouping. Below is the DataFrame I want to obtain. How can I do this in Spark? Either PySpark or SparkR code will work.
#What I want
custId| date | newcust | finaldesc
----------------------------------------------
1001 | 2013-08-01| 1 | New
1001 | 2014-01-01| 1 | Good
1001 | 2014-03-01| 1 | Bad
1002 | 2014-02-01| 1 | Good
1003 | 2014-04-01| 1 | New
推荐答案
我不了解sparkR,所以我将在pyspark中回答. 您可以使用窗口功能来实现.
I don't know for sparkR so I'll answer in pyspark. You can achieve this using window functions.
首先,让我们定义"newcust
的分组",您要使newcust
等于1的每一行都成为新组的开始,计算累计和将达到目的:
First, let's define the "groupings of newcust
", you want every line where newcust
equals 1 to be the start of a new group, computing a cumulative sum will do the trick:
from pyspark.sql import Window
import pyspark.sql.functions as psf
w1 = Window.partitionBy("custId").orderBy("date")
df1 = df.withColumn("subgroup", psf.sum("newcust").over(w1))
+------+----------+----+-------+--------+
|custId| date|desc|newcust|subgroup|
+------+----------+----+-------+--------+
| 1001|2013-08-01| New| 1| 1|
| 1001|2014-01-01| New| 1| 2|
| 1001|2014-02-01|Good| 0| 2|
| 1001|2014-03-01| New| 1| 3|
| 1001|2014-04-01| Bad| 0| 3|
| 1002|2014-02-01| New| 1| 1|
| 1002|2014-03-01|Good| 0| 1|
| 1002|2014-04-01|Good| 0| 1|
| 1003|2014-04-01| New| 1| 1|
+------+----------+----+-------+--------+
对于每个subgroup
,我们要保留第一个日期:
For each subgroup
, we want to keep the first date:
w2 = Window.partitionBy("custId", "subgroup")
df2 = df1.withColumn("first_date", psf.min("date").over(w2))
+------+----------+----+-------+--------+----------+
|custId| date|desc|newcust|subgroup|first_date|
+------+----------+----+-------+--------+----------+
| 1001|2013-08-01| New| 1| 1|2013-08-01|
| 1001|2014-01-01| New| 1| 2|2014-01-01|
| 1001|2014-02-01|Good| 0| 2|2014-01-01|
| 1001|2014-03-01| New| 1| 3|2014-03-01|
| 1001|2014-04-01| Bad| 0| 3|2014-03-01|
| 1002|2014-02-01| New| 1| 1|2014-02-01|
| 1002|2014-03-01|Good| 0| 1|2014-02-01|
| 1002|2014-04-01|Good| 0| 1|2014-02-01|
| 1003|2014-04-01| New| 1| 1|2014-04-01|
+------+----------+----+-------+--------+----------+
最后,我们要保留每个subgroup
的最后一行(按日期排序):
Finally, we want to keep the last line (ordered by date) of every subgroup
:
w3 = Window.partitionBy("custId", "subgroup").orderBy(psf.desc("date"))
df3 = df2.withColumn(
"rn",
psf.row_number().over(w3)
).filter("rn = 1").select(
"custId",
psf.col("first_date").alias("date"),
"desc"
)
+------+----------+----+
|custId| date|desc|
+------+----------+----+
| 1001|2013-08-01| New|
| 1001|2014-01-01|Good|
| 1001|2014-03-01| Bad|
| 1002|2014-02-01|Good|
| 1003|2014-04-01| New|
+------+----------+----+
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