How to count the number of adjacent values in a Pyspark Dataframe equal to a certain value using a rolling window function?

Question

Sample dataframe can be created using:

    from pyspark.sql.functions import col
    from pyspark.sql.window import Window

    df = sc.parallelize([['2019-08-29 01:00:00',0],
                          ['2019-08-29 02:00:00',0],
                          ['2019-08-29 03:00:00',0],
                          ['2019-08-29 04:00:00',1],
                          ['2019-08-29 05:00:00',2],
                          ['2019-08-29 06:00:00',3],
                          ['2019-08-29 07:00:00',0],
                          ['2019-08-29 08:00:00',2],
                          ['2019-08-29 09:00:00',0],
                          ['2019-08-29 10:00:00',1]]).toDF(['DATETIME','VAL']).withColumn('DATETIME',col('DATETIME').cast('timestamp'))

I want to produce a column with a count equal to the number of occurrences of 0 values within a 3 hour period (+/- 1 hour of the current time inclusive of the current Val). The window can be created using:

w1 = (Window()
 .orderBy(col('DATETIME').cast('long'))
 .rangeBetween(-(60*60), 60*60))

Desired outcome:

+-------------------+---+---+
|           DATETIME|VAL|NUM|
+-------------------+---+---+
|2019-08-29 01:00:00|  0|  2|
|2019-08-29 02:00:00|  0|  3|
|2019-08-29 03:00:00|  0|  2|
|2019-08-29 04:00:00|  1|  1|
|2019-08-29 05:00:00|  2|  0|
|2019-08-29 06:00:00|  3|  1|
|2019-08-29 07:00:00|  0|  1|
|2019-08-29 08:00:00|  2|  2|
|2019-08-29 09:00:00|  0|  1|
|2019-08-29 10:00:00|  1|  1|
+-------------------+---+---+

Waqar Ahmed · Accepted Answer · 2020-01-17 10:48:43Z

If you have only 1 entry per DATETIME, you can use lead and lag function to get the previous and next values and then you can count for zeros.

from pyspark.sql.functions import udf, array, col
from pyspark.sql.types import IntegerType

count_zeros_udf = udf(lambda arr: arr.count(0), IntegerType())

df.withColumn('lag1', f.lag(col('VAL'), 1, -1).over(Window.orderBy("DATETIME")))   # Get the previous value
.withColumn('lag2', f.lead(col('VAL'), 1, -1).over(Window.orderBy("DATETIME")))    # Get the next value
.withColumn('NUM', count_zeros_udf(array('VAL', 'lag1', 'lag2')))                  # Count zeros using the udf
.drop('lag1', 'lag2')                                                              # Drop the extra columns
.show()

+-------------------+---+---+
|           DATETIME|VAL|NUM|
+-------------------+---+---+
|2019-08-29 01:00:00|  0|  2|
|2019-08-29 02:00:00|  0|  3|
|2019-08-29 03:00:00|  0|  2|
|2019-08-29 04:00:00|  1|  1|
|2019-08-29 05:00:00|  2|  0|
|2019-08-29 06:00:00|  3|  1|
|2019-08-29 07:00:00|  0|  1|
|2019-08-29 08:00:00|  2|  2|
|2019-08-29 09:00:00|  0|  1|
|2019-08-29 10:00:00|  1|  1|
+-------------------+---+---+

With pyspark >= 2.4, you can use UDF with pandas UDF on window as explained here User defined function to be applied to Window in PySpark? . Unfortunately, I dont have pyspark 2.4 or above, therefore I cannot test it.

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