How to calculate group-based quantiles? - scala

Question

I'm using spark-sql-2.4.1v, and I'm trying to do find quantiles, i.e. percentile 0, percentile 25, etc, on each column of my given data.
My dataframe df:
+----+---------+-------------+----------+-----------+--------+
| id| date| revenue|con_dist_1| con_dist_2| state |
+----+---------+-------------+----------+-----------+--------+
| 10|1/15/2018| 0.010680705| 6|0.019875458| TX |
| 10|1/15/2018| 0.006628853| 4|0.816039063| AZ |
| 10|1/15/2018| 0.01378215| 4|0.082049528| TX |
| 10|1/15/2018| 0.010680705| 6|0.019875458| TX |
| 10|1/15/2018| 0.006628853| 4|0.816039063| AZ |
+----+---------+-------------+----------+-----------+--------+
How to find the quantile on the columns "con_dist_1" & "con_dist_2" for each state?

Answer 1

The possible solution could be:
scala> input.show
+---+---------+-----------+----------+-----------+-----+
| id| date| revenue|con_dist_1| con_dist_2|state|
+---+---------+-----------+----------+-----------+-----+
| 10|1/15/2018|0.010680705| 6|0.019875458| TX|
| 10|1/15/2018|0.006628853| 4|0.816039063| AZ|
| 10|1/15/2018| 0.01378215| 4|0.082049528| TX|
| 10|1/15/2018|0.010680705| 6|0.019875458| TX|
| 10|1/15/2018|0.006628853| 4|0.816039063| AZ|
+---+---------+-----------+----------+-----------+-----+
scala> val df1 = input.groupBy("state").agg(collect_list("con_dist_1").as("combined_1"), collect_list("con_dist_2").as("combined_2"))
df1: org.apache.spark.sql.DataFrame = [state: string, combined_1: array<int> ... 1 more field]
scala> df1.show
+-----+----------+--------------------+
|state|combined_1| combined_2|
+-----+----------+--------------------+
| AZ| [4, 4]|[0.816039063, 0.8...|
| TX| [6, 4, 6]|[0.019875458, 0.0...|
+-----+----------+--------------------+
scala> df1.
| withColumn("comb1_Q1", sort_array($"combined_1")(((size($"combined_1")-1)*0.25).cast("int"))).
| withColumn("comb1_Q2", sort_array($"combined_1")(((size($"combined_1")-1)*0.5).cast("int"))).
| withColumn("comb1_Q3", sort_array($"combined_1")(((size($"combined_1")-1)*0.75).cast("int"))).
| withColumn("comb_2_Q1", sort_array($"combined_2")(((size($"combined_2")-1)*0.25).cast("int"))).
| withColumn("comb_2_Q2", sort_array($"combined_2")(((size($"combined_2")-1)*0.5).cast("int"))).
| withColumn("comb_2_Q3", sort_array($"combined_2")(((size($"combined_2")-1)*0.75).cast("int"))).
| show
+-----+----------+--------------------+--------+--------+--------+-----------+-----------+-----------+
|state|combined_1| combined_2|comb1_Q1|comb1_Q2|comb1_Q3| comb_2_Q1| comb_2_Q2| comb_2_Q3|
+-----+----------+--------------------+--------+--------+--------+-----------+-----------+-----------+
| AZ| [4, 4]|[0.816039063, 0.8...| 4| 4| 4|0.816039063|0.816039063|0.816039063|
| TX| [6, 4, 6]|[0.019875458, 0.0...| 4| 6| 6|0.019875458|0.019875458|0.019875458|
+-----+----------+--------------------+--------+--------+--------+-----------+-----------+-----------+
EDIT
I don't think we can achieve using approx quantile method as you want it for each state for which you will need to group by on state column and aggregate the con_dist columns and approx quantile expects a whole column of integers or float but not of array types.
The other solution is to use spark-sql as shown below:
scala> input.show
+---+---------+-----------+----------+-----------+-----+
| id| date| revenue|con_dist_1| con_dist_2|state|
+---+---------+-----------+----------+-----------+-----+
| 10|1/15/2018|0.010680705| 6|0.019875458| TX|
| 10|1/15/2018|0.006628853| 4|0.816039063| AZ|
| 10|1/15/2018| 0.01378215| 4|0.082049528| TX|
| 10|1/15/2018|0.010680705| 6|0.019875458| TX|
| 10|1/15/2018|0.006628853| 4|0.816039063| AZ|
+---+---------+-----------+----------+-----------+-----+
scala> input.createOrReplaceTempView("input")
scala> :paste
// Entering paste mode (ctrl-D to finish)
val query = "select state, percentile_approx(con_dist_1,0.25) as col1_quantile_1, " +
"percentile_approx(con_dist_1,0.5) as col1_quantile_2," +
"percentile_approx(con_dist_1,0.75) as col1_quantile_3, " +
"percentile_approx(con_dist_2,0.25) as col2_quantile_1,"+
"percentile_approx(con_dist_2,0.5) as col2_quantile_2," +
"percentile_approx(con_dist_2,0.75) as col2_quantile_3 " +
"from input group by state"
// Exiting paste mode, now interpreting.
query: String = select state, percentile_approx(con_dist_1,0.25) as col1_quantile_1, percentile_approx(con_dist_1,0.5) as col1_quantile_2,percentile_approx(con_dist_1,0.75) as col1_quantile_3, percentile_approx(con_dist_2,0.25) as col2_quantile_1,percentile_approx(con_dist_2,0.5) as col2_quantile_2,percentile_approx(con_dist_2,0.75) as col2_quantile_3 from input group by state
scala> val df2 = spark.sql(query)
df2: org.apache.spark.sql.DataFrame = [state: string, col1_quantile_1: int ... 5 more fields]
scala> df2.show
+-----+---------------+---------------+---------------+---------------+---------------+---------------+
|state|col1_quantile_1|col1_quantile_2|col1_quantile_3|col2_quantile_1|col2_quantile_2|col2_quantile_3|
+-----+---------------+---------------+---------------+---------------+---------------+---------------+
| AZ| 4| 4| 4| 0.816039063| 0.816039063| 0.816039063|
| TX| 4| 6| 6| 0.019875458| 0.019875458| 0.082049528|
+-----+---------------+---------------+---------------+---------------+---------------+---------------+
Let me know if it helps!!