DataEngPrep.tech
QuestionsPracticeAI CoachDashboardPacksBlog
ProLogin
Home/Questions/General/Other/Reverse operation for splitting values back to original format

Reverse operation for splitting values back to original format

General/Othermedium0.1 min read

Join back: SQL STRING_AGG(value, ',') or array_to_string(array_agg(col), ','). Python ','.join(list). Spark: groupBy.agg(collect_list).alias('vals').withColumn('restored', concat_ws(',','vals')). Preserve order: array_agg with ORDER BY. Handle nulls....

🤖 Analyze Your Answer
Frequency
Low
Asked at 1 company
Category
243
questions in General/Other
Difficulty Split
151E|43M|49H
in this category
Total Bank
1,863
across 7 categories
Asked at these companies
Pubmatic
Key Concepts Tested
etljoinpythonsparksql

Why This Question Matters

This medium-level General/Other question appears frequently in data engineering interviews at companies like Pubmatic. While less common, it tests deeper understanding that distinguishes strong candidates. Mastering the underlying concepts (etl, join, python) will help you answer variations of this question confidently.

How to Approach This

Break this problem into components. Identify the core trade-offs involved, then walk the interviewer through your reasoning step by step. Demonstrate awareness of edge cases and production considerations - this is what separates good answers from great ones.

Expert Answer
30 words

Join back: SQL STRING_AGG(value, ',') or array_to_string(array_agg(col), ','). Python ','.join(list). Spark: groupBy.agg(collect_list).alias('vals').withColumn('restored', concat_ws(',','vals')). Preserve order: array_agg with ORDER BY. Handle nulls. WHY: Explode/implode symmetry for ETL; order matters for reproducibility.

dataengprep.techdataengprep.techdataengprep.techdataengprep.tech
dataengprep.techdataengprep.techdataengprep.techdataengprep.tech
dataengprep.techdataengprep.techdataengprep.techdataengprep.tech
dataengprep.techdataengprep.techdataengprep.techdataengprep.tech
dataengprep.techdataengprep.techdataengprep.techdataengprep.tech
dataengprep.techdataengprep.techdataengprep.techdataengprep.tech

Want feedback on your answer?

Paste your answer to this question and our AI Coach scores it, finds gaps, and shows you the FAANG-level version.

Try Answer Analyzer →
Want all answers as a PDF for offline study?
1,863 questions across 7 categories — Interview Packs →

Free: Top 20 SQL Interview Questions (PDF)

Get the most asked SQL questions with expert answers. Instant download.

No spam. Unsubscribe anytime.

Related General/Other Questions

hardHave you worked on Data Warehousing projects?FreemediumHow would you read data from a web API? What steps would you follow after reading the data?FreehardRetrieve the most recent sale_timestamp for each product (Latest Transaction).FreehardWhat is the difference between OLTP and OLAP?FreemediumWhat is the difference between SQL and NoSQL databases?Free

Companies that ask this General/Other question

Pubmatic interview questions →

Want to know if YOUR answer is good enough?

Paste your answer and get instant AI feedback with a FAANG-level improved version.

Analyze My Answer — Free

According to DataEngPrep.tech, this is one of the most frequently asked General/Other interview questions, reported at 1 company. DataEngPrep.tech maintains a curated database of 1,863+ real data engineering interview questions across 7 categories, verified by industry professionals.

← Back to all questionsMore General/Other questions →