Below is an example from https://graphframes.github.io/graphframes/docs/_site/user-guide.html
the only thing I confused is the purpose of "lit(0)" from function of condition if this "lit(0)" mean to feed into "cnt"? if yes why is it after ["ab","bc","cd"]?
from pyspark.sql.functions import col, lit, when
from pyspark.sql.types import IntegerType
from graphframes.examples import Graphs
from functools import reduce
chain4 = g.find("(a)-[ab]->(b); (b)-[bc]->(c); (c)-[cd]->(d)")
chain4.show()
sumFriends = lambda cnt,relationship: when(relationship == "friend", cnt+1).otherwise(cnt)
condition = reduce(lambda cnt,e: sumFriends(cnt, col(e).relationship), ["ab", "bc", "cd"], lit(0))
chainWith2Friends2 = chain4.where(condition >= 2)
chainWith2Friends2.show()
lit(0) is the initializer of the reduce statement. You need to initialize the sumFriends counter with cnt = 0 to start counting.
condition = reduce(lambda cnt,e: sumFriends(cnt, col(e).relationship), ["ab", "bc", "cd"], lit(0))
# should be equivalent to
condition = sumFriends(lit(0), col("ab").relationship)
condition = sumFriends(condition, col("bc").relationship)
condition = sumFriends(condition, col("cd").relationship)