Skip to main content

A way to Merge Columns of DataFrames in Spark with no Common Column Key

Made post at Databricks forum, thinking about how to take two DataFrames of the same number of rows and combine, merge, all columns into one DataFrame. This is straightforward, as we can use the monotonically_increasing_id() function to assign unique IDs to each of the rows, the same for each Dataframe. It would be ideal to add extra rows which are null to the Dataframe with fewer rows so they match, although the code below does not do this.

Once the IDs are added, a DataFrame join will merge all the columns into one Dataframe.


# For two Dataframes that have the same number of rows, merge all columns, row by row.

# Get the function monotonically_increasing_id so we can assign ids to each row, when the
# Dataframes have the same number of rows.
from pyspark.sql.functions import monotonically_increasing_id

#Create some test data with 3 and 4 columns.
df1 = sqlContext.createDataFrame([("foo", "bar","too","aaa"), ("bar", "bar","aaa","foo"), ("aaa", "bbb","ccc","ddd")], ("k", "K" ,"v" ,"V"))
df2 = sqlContext.createDataFrame([("aaa", "bbb","ddd"), ("www", "eee","rrr"), ("jjj", "rrr","www")], ("m", "M" ,"n"))

# Add increasing Ids, and they should be the same.
df1 = df1.withColumn("id", monotonically_increasing_id())
df2 = df2.withColumn("id", monotonically_increasing_id())

# Perform a join on the ids.
df3 = df2.join(df1, "id", "outer").drop("id")
df3.show()

Started a GitHub repository as look at code snippets for Apache Spark.



Popular posts from this blog

Darrell Ulm Git Hub Profile Page

This is the software development profile page of Darrell Ulm for GitHub including projects and code for these languages C, C++, PHP, ASM, C#, Unity3d and others. Here is the link: https://github.com/drulm The content can be found at these other sites: Profile , Wordpress , and Tumblr . Certainly we're seeing more and more projects on Github or moving there and wondering how much of the software project domain they currently have percentage-wise.

Apache Spark Knapsack Approximation Algorithm in Python

The code shown below computes an approximation algorithm, greedy heuristic, for the 0-1 knapsack problem in Apache Spark. Having worked with parallel dynamic programming algorithms a good amount, wanted to see what this would look like in Spark. The Github code repo. for the Knapsack approximation algorithms is here , and it includes a Scala solution. The work on a Java version is in progress at time of this writing. Below we have the code that computes the solution that fits within the knapsack W for a set of items each with it's own weight and profit value. We look to maximize the final sum of selected items profits while not exceeding the total possible weight, W. First we import some spark libraries into Python. # Knapsack 0-1 function weights, values and size-capacity. from pyspark.sql import SparkSession from pyspark.sql.functions import lit from pyspark.sql.functions import col from pyspark.sql.functions import sum Now define the function, which will take a Spark ...

Getting back into parallel computing with Apache Spark

Returning to parallel computing with Apache Spark has been insightful, especially observing the increasing mainstream adoption of the McColl and Valiant BSP (Bulk Synchronous Parallel) model beyond GPUs. This structured approach to parallel computation, with its emphasis on synchronized supersteps, offers a practical framework for diverse parallel architectures.While setting up Spark on clusters can involve effort and introduce overhead, ongoing optimizations are expected to enhance its efficiency over time. Improvements in data handling, memory management, and query execution aim to streamline parallel processing.A GitHub repository for Spark snippets has been created as a resource for practical examples. As Apache Spark continues to evolve in parallel with the HDFS (Hadoop Distributed File System), this repository intends to showcase solutions leveraging their combined strengths for scalable data processing.