Appending column name to column value using Spark

问题

I have data in comma separated file, I have loaded it in the spark data frame: The data looks like:

I want to transform the above data frame in spark using pyspark as:

   A    B   C
  A_1  B_2  C_3
  A_4  B_5  C_6
  --------------

Then convert it to list of list using pyspark as:

[[ A_1 , B_2 , C_3],[A_4 , B_5 , C_6]]

And then run FP Growth algorithm using pyspark on the above data set.

The code that I have tried is below:

from pyspark.sql.functions import col, size
from pyspark.sql.functions import *
import pyspark.sql.functions as func
from pyspark.sql.functions import udf
from pyspark.sql.types import StringType
from pyspark.ml.fpm import FPGrowth
from pyspark.sql import Row
from pyspark.context import SparkContext
from pyspark.sql.session import SparkSession
from pyspark import SparkConf
from pyspark.sql.types import StringType
from pyspark import SQLContext

sqlContext = SQLContext(sc)
df = spark.read.format("csv").option("header", "true").load("dbfs:/FileStore/tables/data.csv")

 names=df.schema.names

Then I thought of doing something inside for loop:

 for name in names:
      -----
      ------

After this I will be using fpgrowth:

df = spark.createDataFrame([
    (0, [ A_1 , B_2 , C_3]),
    (1, [A_4 , B_5 , C_6]),)], ["id", "items"])

fpGrowth = FPGrowth(itemsCol="items", minSupport=0.5, minConfidence=0.6)
model = fpGrowth.fit(df)

回答1:

A number of concepts here for those who use Scala normally showing how to do with pyspark. Somewhat different but learnsome for sure, although to how many is the big question. I certainly learnt a point on pyspark with zipWithIndex myself. Anyway.

First part is to get stuff into desired format, probably too may imports but leaving as is:

from functools import reduce
from pyspark.sql.functions import lower, col, lit, concat, split
from pyspark.sql.types import * 
from pyspark.sql import Row
from pyspark.sql import functions as f

source_df = spark.createDataFrame(
   [
    (1, 11, 111),
    (2, 22, 222)
   ],
   ["colA", "colB", "colC"]
                                 )

intermediate_df = (reduce(
                    lambda df, col_name: df.withColumn(col_name, concat(lit(col_name), lit("_"), col(col_name))),
                    source_df.columns,
                    source_df
                   )     )

allCols = [x for x in intermediate_df.columns]
result_df = intermediate_df.select(f.concat_ws(',', *allCols).alias('CONCAT_COLS'))

result_df = result_df.select(split(col("CONCAT_COLS"), ",\s*").alias("ARRAY_COLS"))

# Add 0,1,2,3, ... with zipWithIndex, we add it at back, but that does not matter, you can move it around.
# Get new Structure, the fields (one in this case but done flexibly, plus zipWithIndex value.
schema = StructType(result_df.schema.fields[:] + [StructField("index", LongType(), True)])

# Need this dict approach with pyspark, different to Scala.
rdd = result_df.rdd.zipWithIndex()
rdd1 = rdd.map(
               lambda row: tuple(row[0].asDict()[c] for c in schema.fieldNames()[:-1]) + (row[1],)
              )

final_result_df = spark.createDataFrame(rdd1, schema)
final_result_df.show(truncate=False)

returns:

 +---------------------------+-----+
 |ARRAY_COLS                 |index|
 +---------------------------+-----+
 |[colA_1, colB_11, colC_111]|0    |
 |[colA_2, colB_22, colC_222]|1    |
 +---------------------------+-----+

Second part is the old zipWithIndex with pyspark if you need 0,1,.. Painful compared to Scala.

In general easier to solve in Scala.

Not sure on performance, not a foldLeft, interesting. I think it is OK actually.

来源：https://stackoverflow.com/questions/57459741/appending-column-name-to-column-value-using-spark

标签

pyspark

apache-spark-sql

azure-databricks

fpgrowth