Pyspark Dynamic Column Computation

Below is my spark data frame a b c 1 3 4 2 0 0 4 1 0 2 2 0 My output should be as below a b c 1 3 4 2 0 2 4 1 -1 2 2 3 Formula is prev(c)-b+a i.e, 4-2+0=2 and 2-4+1=-1

Solution 1:

from pyspark.sql.functions import lag, udf
from pyspark.sql.types import IntegerType
from pyspark.sql.window import Window

numbers = [[1,2,3],[2,3,4],[3,4,5],[5,6,7]]
df = sc.parallelize(numbers).toDF(['a','b','c'])
df.show()

w = Window().partitionBy().orderBy('a')
calculate = udf(lambda a,b,c:a-b+c,IntegerType())
df = df.withColumn('result', lag("a").over(w)-df.b+df.c)
df.show()



+---+---+---+
|  a|  b|  c|
+---+---+---+
|  1|  2|  3|
|  2|  3|  4|
|  3|  4|  5|
|  5|  6|  7|
+---+---+---+

+---+---+---+------+
|  a|  b|  c|result|
+---+---+---+------+
|  1|  2|  3|  null|
|  2|  3|  4|     2|
|  3|  4|  5|     3|
|  5|  6|  7|     4|
+---+---+---+------+

Solution 2:

import pyspark.sql.functions as f
from pyspark.sql.window import Window

df = sc.parallelize([
    [1,3],
    [2,0],
    [4,1],
    [2,2]
]).toDF(('a', 'b'))

df1 = df.withColumn("row_id", f.monotonically_increasing_id())
w = Window.partitionBy().orderBy(f.col("row_id"))
df1 = df1.withColumn("c_temp", f.when(f.col("row_id")==0, f.lit(4)).otherwise(- f.col("a") + f.col("b")))
df1 = df1.withColumn("c", f.sum(f.col("c_temp")).over(w)).drop("c_temp","row_id")
df1.show()

Output is:

+---+---+---+
|  a|  b|  c|
+---+---+---+
|  1|  3|  4|
|  2|  0|  2|
|  4|  1| -1|
|  2|  2| -1|
+---+---+---+