CODEWITHSUNDEEP
pythonpysparklaglead
SatZ
SatZ

Reputation: 450

pyspark lag function on one column based on the value in another column

I want to be able to create a lag value based on the value in one of the columns.

in the data given Qdf is the Question dataframe and Adf the Answer dataframe. I have given an additional explanation column (which I actually dont need in my final data)

from pyspark.sql.window import Window
import pyspark.sql.functions as func
from pyspark.sql.types import *
from pyspark.sql import SQLContext

ID = ['A' for i in range(0,10)]+ ['B' for i in range(0,10)]
Day = range(1,11)+range(1,11)
Delay = [2, 2, 2, 3, 2, 4, 3, 2, 2, 2, 2, 2, 3, 2, 4, 3, 2, 2, 2, 3]
Despatched = [2, 3, 1, 4, 6, 2, 6, 5, 3, 6, 3, 1, 2, 4, 1, 2, 3, 3, 6, 1]
Delivered = [0, 0, 2, 3, 1, 0, 10, 0, 0, 13, 0, 0, 3, 1, 0, 6, 0, 0, 6, 3]
Explanation = ["-", "-", "-", "-", "-", "-", "10 (4+6)", "-", "-", "13 (2+6+5)", "-", "-", "-", "-", "-", "6 (2+4)", "-", "-", "6 (1+2+3)", "-"]

QSchema = StructType([StructField("ID", StringType()),StructField("Day", IntegerType()),StructField("Delay", IntegerType()),StructField("Despatched", IntegerType())])
Qdata = map(list, zip(*[ID,Day,Delay,Despatched]))
Qdf = spark.createDataFrame(Qdata,schema=QSchema) 
Qdf.show()


+---+---+-----+----------+
| ID|Day|Delay|Despatched|
+---+---+-----+----------+
|  A|  1|    2|         2|
|  A|  2|    2|         3|
|  A|  3|    2|         1|
|  A|  4|    3|         4|
|  A|  5|    2|         6|
|  A|  6|    4|         2|
|  A|  7|    3|         6|
|  A|  8|    2|         5|
|  A|  9|    2|         3|
|  A| 10|    2|         6|
|  B|  1|    2|         3|
|  B|  2|    2|         1|
|  B|  3|    3|         2|
|  B|  4|    2|         4|
|  B|  5|    4|         1|
|  B|  6|    3|         2|
|  B|  7|    2|         3|
|  B|  8|    2|         3|
|  B|  9|    2|         6|
|  B| 10|    3|         1|
+---+---+-----+----------+

The despatched quantity should be recorded as delivered after the delay time. Ideally it would be great if I can apply the lag function on the despatched column based on the delay. The Answer dataset would look like below:

Adata = map(list, zip(*[ID,Day,Delay,Despatched,Delivered,Explanation]))
ASchema = StructType([StructField("ID", StringType()),StructField("Day", IntegerType()),StructField("Delay", IntegerType()),StructField("Despatched", IntegerType()),StructField("Delivered", IntegerType()),StructField("Explanation", StringType())])
Adf = spark.createDataFrame(Adata,schema=ASchema) 
Adf.show()

+---+---+-----+----------+---------+-----------+
| ID|Day|Delay|Despatched|Delivered|Explanation|
+---+---+-----+----------+---------+-----------+
|  A|  1|    2|         2|        0|          -|
|  A|  2|    2|         3|        0|          -|
|  A|  3|    2|         1|        2|          -|
|  A|  4|    3|         4|        3|          -|
|  A|  5|    2|         6|        1|          -|
|  A|  6|    4|         2|        0|          -|
|  A|  7|    3|         6|       10|   10 (4+6)|
|  A|  8|    2|         5|        0|          -|
|  A|  9|    2|         3|        0|          -|
|  A| 10|    2|         6|       13| 13 (2+6+5)|
|  B|  1|    2|         3|        0|          -|
|  B|  2|    2|         1|        0|          -|
|  B|  3|    3|         2|        3|          -|
|  B|  4|    2|         4|        1|          -|
|  B|  5|    4|         1|        0|          -|
|  B|  6|    3|         2|        6|    6 (2+4)|
|  B|  7|    2|         3|        0|          -|
|  B|  8|    2|         3|        0|          -|
|  B|  9|    2|         6|        6|  6 (1+2+3)|
|  B| 10|    3|         1|        3|          -|
+---+---+-----+----------+---------+-----------+

I have tried the below code to get a constant lag of 2:

Qdf1=Qdf.withColumn('Delivered_lag',func.lag(Qdf['Despatched'],2).over(Window.partitionBy("ID").orderBy("Day")))

But, when I try to use lag on one column and lag by another column I get the error: 

Qdf1=Qdf.withColumn('Delivered_lag',func.lag(Qdf['Despatched'],Qdf['Delay']).over(Window.partitionBy("ID").orderBy("Day")))

TypeError: 'Column' object is not callable

How can I get past this? I am using PySpark version 2.3.1 and python version 2.7.13.

Upvotes: 1

Views: 4768

Answers (1)

cronoik
cronoik

Reputation: 19540

The lag-function takes a fixed value as count parameter, but what you can do is to create a loop with when and otherwise to get what you want:

from pyspark.sql.window import Window
import pyspark.sql.functions as F
import pyspark.sql.types as T 

ID = ['A' for i in range(0,10)]+ ['B' for i in range(0,10)]
#I had to modify this line as I'am working with python3
Day = list(range(1,11))+list(range(1,11))
Delay = [2, 2, 2, 3, 2, 4, 3, 2, 2, 2, 2, 2, 3, 2, 4, 3, 2, 2, 2, 3]
Despatched = [2, 3, 1, 4, 6, 2, 6, 5, 3, 6, 3, 1, 2, 4, 1, 2, 3, 3, 6, 1]
Delivered = [0, 0, 2, 3, 1, 0, 10, 0, 0, 13, 0, 0, 3, 1, 0, 6, 0, 0, 6, 3]
Explanation = ["-", "-", "-", "-", "-", "-", "10 (4+6)", "-", "-", "13 (2+6+5)", "-", "-", "-", "-", "-", "6 (2+4)", "-", "-", "6 (1+2+3)", "-"]

QSchema = T.StructType([T.StructField("ID", T.StringType()),T.StructField("Day", T.IntegerType()),T.StructField("Delay", T.IntegerType()),T.StructField("Despatched", T.IntegerType())])
Qdata = map(list, zip(*[ID,Day,Delay,Despatched]))
Qdf = spark.createDataFrame(Qdata,schema=QSchema) 
#until here it was basically your code

#At first we add an empty Delivered_lag column to the Qdf
#That allows us to use the same functionality for all iterations of the following loop
Qdf = Qdf.withColumn('Delivered_lag',  F.lit(None).cast(T.IntegerType()))

#Now we loop over the distinctive values of Qdf.delay and run the lag function for every value
#otherwise is necessary to keep the previous calculated values 
for delay in Qdf.select('delay').distinct().collect():
    Qdf = Qdf.withColumn('Delivered_lag', F.when(Qdf['Delay'] == delay.delay, F.lag(Qdf['Despatched'],delay.delay).over(Window.partitionBy("ID").orderBy("Day"))).otherwise(Qdf['Delivered_lag']))

Qdf.show()

Output:

+---+---+-----+----------+-------------+ 
| ID|Day|Delay|Despatched|Delivered_lag|
+---+---+-----+----------+-------------+ 
|  B|  1|    2|         3|         null|
|  B|  2|    2|         1|         null|
|  B|  3|    3|         2|         null| 
|  B|  4|    2|         4|            1| 
|  B|  5|    4|         1|            3| 
|  B|  6|    3|         2|            2| 
|  B|  7|    2|         3|            1| 
|  B|  8|    2|         3|            2| 
|  B|  9|    2|         6|            3| 
|  B| 10|    3|         1|            3| 
|  A|  1|    2|         2|         null| 
|  A|  2|    2|         3|         null| 
|  A|  3|    2|         1|            2| 
|  A|  4|    3|         4|            2| 
|  A|  5|    2|         6|            1| 
|  A|  6|    4|         2|            3| 
|  A|  7|    3|         6|            4| 
|  A|  8|    2|         5|            2| 
|  A|  9|    2|         3|            6| 
|  A| 10|    2|         6|            5| 
+---+---+-----+----------+-------------+

Upvotes: 2

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