Pyspark : how to code complicated dataframe calculation lead sum

问题

I have given dataframe that looks like this. THIS dataframe is sorted by date, and col1 is just some random value.

    TEST_schema = StructType([StructField("date", StringType(), True),\
                              StructField("col1", IntegerType(), True),\
                             ])
    TEST_data = [('2020-08-01',3),('2020-08-02',1),('2020-08-03',-1),('2020-08-04',-1),('2020-08-05',3),\
                 ('2020-08-06',-1),('2020-08-07',6),('2020-08-08',4),('2020-08-09',5)]
    rdd3 = sc.parallelize(TEST_data)
    TEST_df = sqlContext.createDataFrame(TEST_data, TEST_schema)
    TEST_df.show() 
    
+----------+----+
|      date|col1|
+----------+----+
|2020-08-01|   3|
|2020-08-02|   1|
|2020-08-03|  -1|
|2020-08-04|  -1|
|2020-08-05|   3|
|2020-08-06|  -1|
|2020-08-07|   6|
|2020-08-08|   4|
|2020-08-09|   5|
+----------+----+

LOGIC : lead(col1) +1, if col1 ==-1, then from the previous value lead(col1) +2...
the resulted dataframe will look like this (want column is what i want as output)

+----------+----+----+
|      date|col1|WANT|
+----------+----+----+
|2020-08-01|   3|   2|
|2020-08-02|   1|   6|
|2020-08-03|  -1|   5|
|2020-08-04|  -1|   4|
|2020-08-05|   3|   8|
|2020-08-06|  -1|   7|
|2020-08-07|   6|   5|
|2020-08-08|   4|   6|
|2020-08-09|   5|  -1|
+----------+----+----+

Let's look at last row, where col1==5, that 5 is leaded +1 which is in want==6 (2020-08-08) If we have col==-1, then we add +1 more ,, if we have col==-1 repeated twice, then we add +2 more.. this is hard to explain in words,lastly since it created last column instead of null, replace with -1. I have a diagram

回答1:

You can check if the following code and logic works for you:

create a sub-group label g which take running sum of int(col1!=-1), and we only concern about Rows with col1 == -1, and nullify all other Rows.
the residual is 1 and if col1 == -1, plus the running count on Window w2
take the prev_col1 over w1 which is not -1 (using nullif), (the naming of prev_col1 might be confusion since it takes only if col1 = -1 using typical pyspark's way to do ffill, otherwise keep the original).
set val = prev_col1 + residual, take the lag and set null to -1

Code below:

from pyspark.sql.functions import when, col, expr, count, desc, lag, coalesce    
from pyspark.sql import Window

w1 = Window.orderBy(desc('date'))
w2 = Window.partitionBy('g').orderBy(desc('date'))  

TEST_df.withColumn('g', when(col('col1') == -1, expr("sum(int(col1!=-1))").over(w1))) \
    .withColumn('residual', when(col('col1') == -1, count('*').over(w2) + 1).otherwise(1)) \
    .withColumn('prev_col1',expr("last(nullif(col1,-1),True)").over(w1)) \
    .withColumn('want', coalesce(lag(expr("prev_col1 + residual")).over(w1),lit(-1))) \
    .orderBy('date').show()
+----------+----+----+--------+---------+----+
|      date|col1|   g|residual|prev_col1|want|
+----------+----+----+--------+---------+----+
|2020-08-01|   3|null|       1|        3|   2|
|2020-08-02|   1|null|       1|        1|   6|
|2020-08-03|  -1|   4|       3|        3|   5|
|2020-08-04|  -1|   4|       2|        3|   4|
|2020-08-05|   3|null|       1|        3|   8|
|2020-08-06|  -1|   3|       2|        6|   7|
|2020-08-07|   6|null|       1|        6|   5|
|2020-08-08|   4|null|       1|        4|   6|
|2020-08-09|   5|null|       1|        5|  -1|
+----------+----+----+--------+---------+----+

来源：https://stackoverflow.com/questions/63308490/pyspark-how-to-code-complicated-dataframe-calculation-lead-sum

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pyspark

apache-spark-sql

pyspark-dataframes