Partition pyspark dataframe based on the change in column value

问题

I have a dataframe in pyspark. Say the has some columns a,b,c... I want to group the data into groups as the value of column changes. Say

A  B
1  x
1  y
0  x
0  y
0  x
1  y
1  x
1  y

There will be 3 groups as (1x,1y),(0x,0y,0x),(1y,1x,1y) And corresponding row data

回答1:

If I understand correctly you want to create a distinct group every time column A changes values.

First we'll create a monotonically increasing id to keep the row order as it is:

import pyspark.sql.functions as psf
df = sc.parallelize([[1,'x'],[1,'y'],[0,'x'],[0,'y'],[0,'x'],[1,'y'],[1,'x'],[1,'y']])\
    .toDF(['A', 'B'])\
    .withColumn("rn", psf.monotonically_increasing_id())
df.show()

    +---+---+----------+
    |  A|  B|        rn|
    +---+---+----------+
    |  1|  x|         0|
    |  1|  y|         1|
    |  0|  x|         2|
    |  0|  y|         3|
    |  0|  x|8589934592|
    |  1|  y|8589934593|
    |  1|  x|8589934594|
    |  1|  y|8589934595|
    +---+---+----------+

Now we'll use a window function to create a column that contains 1 every time column A changes:

from pyspark.sql import Window
w = Window.orderBy('rn')
df = df.withColumn("changed", (df.A != psf.lag('A', 1, 0).over(w)).cast('int'))

    +---+---+----------+-------+
    |  A|  B|        rn|changed|
    +---+---+----------+-------+
    |  1|  x|         0|      1|
    |  1|  y|         1|      0|
    |  0|  x|         2|      1|
    |  0|  y|         3|      0|
    |  0|  x|8589934592|      0|
    |  1|  y|8589934593|      1|
    |  1|  x|8589934594|      0|
    |  1|  y|8589934595|      0|
    +---+---+----------+-------+

Finally we'll use another window function to allocate different numbers to each group:

df = df.withColumn("group_id", psf.sum("changed").over(w)).drop("rn").drop("changed")

    +---+---+--------+
    |  A|  B|group_id|
    +---+---+--------+
    |  1|  x|       1|
    |  1|  y|       1|
    |  0|  x|       2|
    |  0|  y|       2|
    |  0|  x|       2|
    |  1|  y|       3|
    |  1|  x|       3|
    |  1|  y|       3|
    +---+---+--------+

Now you can build you groups

来源：https://stackoverflow.com/questions/47014555/partition-pyspark-dataframe-based-on-the-change-in-column-value

标签

python

dataframe

pyspark

spark-dataframe