wip-add-kurtosis-support-demo

from sparklingpandas.custom_functions import *
import random
input = range(1,6) + range(1,6) + range(1,6) + range(1,6) + range(1,6) + range(1,6)
df1 = sqlContext.createDataFrame(sc.parallelize(input)\
                                    .map(lambda i: Row(single=i, rand= random.randint(0,100000))))
df1.collect()
import pyspark.sql.functions as F
x = df1.groupBy(df1.single).agg(F.min(df1.rand))
x.collect()
j = df1.groupBy(df1.single).agg(kurtosis(df1.rand))
j.collect()