Data Challenge

Data challenges or sometimes called take-home challenges are often sent to a candidate in the initial screening.

You are usually given a few tables with, generally speaking, open questions to demo your skills in the following area:

1. Basic data processing in R/Python or sometimes even SQL

Are you able to transform data before feeding them into a machine learning model?

For example: converting categorical variables into numerical columns; Handle missing values, what to do if there are missing values in specific columns. 

Spot obvious data errors based on logic or intuition, never assume the data is correct, fix it before use it.

2. Code quality

No one wants to review your code if you are hired and checked in poor quality code; 

Don't use crazy lambda functions combined with map-reduce and map to make yourself look smart. Instead, use long variable names that are meaningful, easier to understand.

3. Business and product sense 

Are you able to understand the business context? Do your conclusion and insights make business sense?

4. Clear communication

What is your conclusion, can everyone understand what you try to convey, and what do you recommend for the next steps.

You will often be asked to give a talk during the final round of interviews and answer the hiring team's questions.

5. Machine learning modeling skills

Can you build a classification model and evaluate its performance, what feature engineering steps worked the best, what are the metrics you used, did you run cross-validation to get an unbiased estimate of those metrics, etc.

6. Data visualization

One image is worth a thousand words, especially when you are constantly in meetings with non-technical people. Can you create an informative chart or graph to represent the data? Are you good with ggplot or seaborn?

Our mentors have conducted hundreds of take-home data challenges. Feel free to hire one and get 100% data challenge ready.

  • Founder of, and
  • Most recently a senior manager at Apple, where I built and hired a world-class machine learning team of data scientists, software engineers, data engineers, and product managers.
  • Head of data science at Chegg, research scientist at Amazon, serial entrepreneur.

“I have given many take-home data challenges to candidates as a hiring manager.”

$ 299 ⏰ 1 hour

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⏰ Data Challenge with Leon Wei for $299

  • I am an analytics veteran with over twenty years of experience in driving business value from data.
  • Prior to launching my own practice Intellego Consulting, I built and lead many high-performing data analytics teams at marquee global technology companies. As a player-coach, I have hands-on knowledge of how things work while at the same time being adept at driving outcome and impact. I am passionate about helping motivated early-career technology workers achieve their potential.
$ 299 ⏰ 1 hour

Get access to Chen Zhao's calendar after Stripe process your payment, fully refundable if not 100% satisfied.

⏰ Data Challenge with Chen Zhao for $299

  • Mike is an experienced data engineer, designing and maintaining systems consisting of hundreds of terabytes of data.
$ 299 ⏰ 1 hour

Get access to Mike Metzger's calendar after Stripe process your payment, fully refundable if not 100% satisfied.

⏰ Data Challenge with Mike Metzger for $299

  • Alex is a Principal Product Manager at Sambanova Systems. Previously, Alex has held product management roles at building out their ML Platform and deep learning offering to enterprise customers. He was also an ML practitioner as the first data science hire at Uber’s Advanced Technologies Group working on building large-scale computer vision and sensor fusion algorithms for self-driving cars. Alex is motivated to help raise the next generation of data scientists and product leaders

“UBER ATG's first data scientist, with many years of experience in data science and machine learning.”

$ 299 ⏰ 1 hour

Get access to Alex Chao's calendar after Stripe process your payment, fully refundable if not 100% satisfied.

⏰ Data Challenge with Alex Chao for $299

The easiest way to accomplish something is to hire someone who's done it

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Thank you so much @Leon !

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Joey Huang

Machine Learning Engineer

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Hi @Leon and @Mike ,

Just wanted to share, I accepted an offer from Apple as a Data Engineer and wanted to offer a huge thank you to both of you guys.

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Some of the questions you gave during our Data Modeling with you Mike were presented verbatim.


Data Engineer at Apple

The mock interview helped me do it in the right way

I did a SQL Mock interview on Instamentor to gain a better understanding of how SQL interviews are conducted.

Leon (my mentor) came prepared with a realistic case study example tailored specifically towards the company I was interested in. Read more...

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My actual interview went in a similar manner and having done the mock interview helped me do it in the right way.

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Data Engineer at Square

Extremely valuable!

Shoutout to Leon Wei from

Please do reach out to him if you're looking for career advice, general consulting, or resume feedback. I found his services extremely valuable.

And while you're at it, please do check out SQLPad if you're looking to refresh your SQL concepts.

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Data Science Manager at Swiggy

Recommending him!

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Feng Xue

Senior Data Engineer at T-Mobile

Dream Data Scientist job offer!

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Data Scientist

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I signed up on Leon's service and was pleasantly surprised when he helped me out personally on the website. In two mock interviews with him from, he was meticulously prepared and very professional.

Throughout the interview he provided fantastic feedback and frameworks on how to be better prepared for both technical and behavioural aspects of an interview.

He is also a very positive and friendly person and I enjoyed all my interactions with him.

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Rahul Nayak

Marketing Analyst

Thank you!

Shoutout to Leon Wei from, recommending him if you are searching for great advices and mentorship for you #datascience career.

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Bara Ndiaye

Data Scientist

What made the session successful was the effortlessness in being honest around Leon.

I had my first mentoring call yesterday. The session was to be for 45 mins but lucky for me, Leon did not have a hard stop. We had a detailed discussion around my career history, career transition, stuff I’m good at and enjoy doing/good at but don’t enjoy/not good at and want to improve, not good at and not interested in get the drift). Read more

Leon listened patiently, highlighted areas I needed to work on, pointed out practical considerations, and made gentle suggestions on handling a couple of situations I had bombed (salary negotiation was one).

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Data Scientist

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Data Scientist, received a dream offer

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Data Engineer

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Data Analyst