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Shopify·Data Scientist·Technical Phone Screen·Intermediate

IntermediatePrefer not to say
Jun 2026Remote

Summary

Shopify data scientist interview with a coding-heavy technical screen built around a surprisingly fun scenario involving pirate themes. Three-part question that escalated from basic Python to system design pretty fast.

Questions Asked (3)

Q1

Write a Python function that computes Jaccard similarity between two lists, defined as the length of their intersection divided by the length of their union.

Algorithms & Data Structures
Author's notes

Part A was fine.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the definition of Jaccard similarity and edge cases (e.g., empty lists). Then, implement the function using sets for efficient intersection and union, and discuss time/space complexity. Finally, test with examples to ensure correctness.

Pro tip: Mention that Jaccard similarity is often used in recommendation systems and near-duplicate detection, and that handling duplicates in the input lists (by converting to sets) is crucial because the definition assumes sets.

1. Clarify requirements and edge cases

Confirm that the function should treat lists as sets (ignoring duplicates and order) and handle empty lists (return 0 or 1?). Discuss whether to return a float or handle division by zero.

2. Choose data structures

Use Python sets for efficient intersection and union operations. Convert both lists to sets to remove duplicates and enable O(1) average membership checks.

3. Implement the function

Compute intersection size using set intersection (&) and union size using set union (|). Return intersection size divided by union size, with a guard for empty union.

4. Analyze complexity

Explain that time complexity is O(n + m) on average for set construction and operations, and space complexity is O(n + m) for the sets.

5. Test with examples

Provide test cases: identical lists (similarity 1), disjoint lists (0), partial overlap, and empty lists. Verify results.

Key Points to Mention

  • Definition of Jaccard similarity: |A ∩ B| / |A ∪ B|
  • Handling duplicates: convert lists to sets to ignore duplicates
  • Edge case: empty lists (union size 0) — return 0 or handle gracefully
  • Time and space complexity: O(n + m) average time, O(n + m) space
  • Use of Python set operations: intersection (&) and union (|)
  • Potential applications: recommendation systems, near-duplicate detection, clustering

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.

Q2

Given a list of pirate themes and a list of custom themes (each as a dictionary), return all custom themes whose Jaccard similarity to at least one pirate theme exceeds a given threshold.

Algorithms & Data StructuresProduct Analytics & Metrics
Author's notes

Part B is where things got messier for me.

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AI HintsAI Generated

Suggested Approach

Clarify the input format and similarity definition, then outline an efficient algorithm using sets and inverted indices to avoid pairwise comparisons. Discuss complexity and potential optimizations for large-scale data, and mention how this applies to product analytics at Shopify.

Pro tip: Emphasize that in production, you'd likely use an inverted index or MinHash for scalability, and always validate with edge cases like empty sets or threshold boundaries.

1. Clarify requirements and assumptions

Confirm the structure of theme dictionaries (e.g., keys like 'name' and 'keywords'), the similarity threshold, and whether themes are represented as sets of keywords. Ask about data scale and performance expectations.

2. Define Jaccard similarity and preprocessing

Explain Jaccard similarity as |A ∩ B| / |A ∪ B|. Preprocess each theme into a set of tokens (e.g., lowercase, remove stopwords) to ensure consistent comparison.

3. Design an efficient matching algorithm

Use an inverted index from tokens to pirate themes to quickly find candidate pirate themes for each custom theme. Compute Jaccard similarity only for candidates, and filter by threshold.

4. Analyze complexity and discuss optimizations

Analyze time and space complexity. Mention that inverted index reduces comparisons from O(N*M) to near O(total tokens). For very large scale, suggest MinHash or LSH for approximate similarity.

5. Validate and test edge cases

Test with empty sets, identical sets, disjoint sets, and threshold boundaries. Ensure the solution handles multiple pirate themes and returns unique custom themes.

Key Points to Mention

  • Jaccard similarity formula and its interpretation
  • Set operations and tokenization preprocessing
  • Inverted index for efficient candidate retrieval
  • Time and space complexity analysis
  • Scalability considerations (e.g., MinHash, LSH)
  • Edge cases: empty sets, threshold values, duplicates

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.

Q3

How would you handle edge cases in this similarity computation, and how would you scale it to millions of themes?

System DesignTechnical Trade-offs
Author's notes

This is the part I kind of fumbled.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the similarity metric and data characteristics, then systematically address edge cases with robust preprocessing and fallback strategies. For scaling, propose a distributed architecture using approximate nearest neighbor search and discuss trade-offs between accuracy and efficiency.

Pro tip: Emphasize the importance of monitoring and iterative refinement: start with a simple baseline, measure performance, and optimize bottlenecks. This shows you prioritize business impact over premature optimization.

1. Clarify Requirements and Data

Ask about the similarity metric, data size, dimensionality, and expected query patterns to tailor your approach.

2. Identify and Handle Edge Cases

List potential edge cases (e.g., empty vectors, duplicates, outliers) and propose preprocessing, fallback methods, or special-case handling.

3. Design Scalable Architecture

Outline a distributed pipeline with approximate nearest neighbor search (e.g., FAISS, Annoy) and discuss partitioning, caching, and parallelization.

4. Evaluate Trade-offs

Compare exact vs. approximate methods, latency vs. accuracy, and cost vs. performance, aligning with business needs.

5. Monitor and Iterate

Propose metrics for quality and performance, and describe how to continuously improve the system based on feedback.

Key Points to Mention

  • Cosine similarity vs. Euclidean distance and when to use each
  • Handling missing or sparse data with imputation or dimensionality reduction
  • Approximate nearest neighbor algorithms (e.g., HNSW, LSH) for scalability
  • Distributed computing frameworks (e.g., Spark, Dask) for batch processing
  • Caching and indexing strategies for low-latency queries
  • Trade-offs between exact and approximate methods in terms of accuracy and speed

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.