Removing Duplicate Values in a Hive Table

As data analysts and developers, we often encounter tables with duplicate values that need to be removed or cleaned up. In this article, we will explore how to remove duplicate values from a cell in a Hive table.

Understanding the Problem

The problem at hand is to remove duplicates from a comma-separated list of values in a Hive SQL table. The input data looks something like this:

The expected output is:

Solution Overview

To solve this problem, we will use a combination of Hive’s string manipulation functions and data aggregation techniques. The general approach is to split the comma-separated list into an array, remove duplicates from the array using collect_set, and then concatenate the resulting set back into a single string.

Step 1: Splitting the Comma-Separated List

First, we need to split the comma-separated list into an array. We can use Hive’s lateral view outer explode function to achieve this. Here’s how it works:

• The split(colname, ',') function splits the string colname at each comma character and returns a table with two columns: elem and _1.
• The lateral view outer clause tells Hive to create a derived table that contains all the rows from both tables (in this case, the original table and the exploded table).
• The as elem alias gives the first column of the exploded table an alias called elem.

Here’s the code snippet:

with your_table as(
    select stack(3,
        1, 'test, test1, test,test1',
        2, 'rest,rest1,rest1,rest',   
        3, 'chest,nest,lest,gest'
    ) as (id, colname)
)

select t.id, t.colname, concat_ws(',', collect_set(trim(e.elem))) result
from your_table t
lateral view outer explode(split(colname, ',')) e as elem
group by t.id, t.colname

Step 2: Removing Duplicates from the Array

Next, we use Hive’s collect_set function to remove duplicates from the array. Here’s how it works:

• The collect_set function takes an input table and returns a set of unique values.
• We use the trim(e.elem) expression to remove any leading or trailing whitespace from each element in the array.

Here’s the updated code snippet:

with your_table as(
    select stack(3,
        1, 'test, test1, test,test1',
        2, 'rest,rest1,rest1,rest',   
        3, 'chest,nest,lest,gest'
    ) as (id, colname)
)

select t.id, t.colname, concat_ws(',', collect_set(trim(e.elem))) result
from your_table t
lateral view outer explode(split(colname, ',')) e as elem
group by t.id, t.colname

Step 3: Concatenating the Resulting Set

Finally, we use Hive’s concat_ws function to concatenate the resulting set back into a single string. Here’s how it works:

• The concat_ws function takes two or more input strings and concatenates them with the specified delimiter (in this case, a comma).
• We use the collect_set expression to get an array of unique values from the previous step.

Here’s the final code snippet:

with your_table as(
    select stack(3,
        1, 'test, test1, test,test1',
        2, 'rest,rest1,rest1,rest',   
        3, 'chest,nest,lest,gest'
    ) as (id, colname)
)

select t.id, t.colname, concat_ws(',', collect_set(trim(e.elem))) result
from your_table t
lateral view outer explode(split(colname, ',')) e as elem
group by t.id, t.colname

Conclusion

In this article, we explored how to remove duplicate values from a cell in a Hive table. We used a combination of Hive’s string manipulation functions and data aggregation techniques to achieve the desired result. The final code snippet demonstrates the complete solution using lateral view outer explode, collect_set, and concat_ws. By following this approach, you can easily clean up duplicate values from your Hive tables and improve data quality.

Last modified on 2024-09-07