Solving Real-World Data Science Interview Questions! (with Python Pandas)

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In this video we solve a series of Data Science Interview questions on Stratascratch. We start with easy problems using Python Pandas and then progressively get more difficult. At the end of the video we do five non-coding interview questions that force you to think at a high level.
Mentioned Resources!
Second Channel: / techtrekbykeithgalli
Regex Cheat Sheet: cheatography.com/davechild/ch...
Probability text book: www.amazon.com/dp/188652923X/...
Here are the questions that we complete (in order)
~~ Coding ~~
1. Finding Updated Records: platform.stratascratch.com/co...
2. Number of Bathrooms and Bedrooms: platform.stratascratch.com/co...
3. Counting Instances in Text: platform.stratascratch.com/co...
4. Customer Revenue in March: platform.stratascratch.com/co...
5. Monthly Percentage Difference: platform.stratascratch.com/co...
6. Premium vs Freemium: platform.stratascratch.com/co...
~~ Non-Coding ~~
1. Credit Card Activity: platform.stratascratch.com/te...
2. Outliers Detection: platform.stratascratch.com/te...
3. Probability of Having a Sister: platform.stratascratch.com/te...
4. Uber Black Rides: platform.stratascratch.com/te...
5. Terabyte of Data: platform.stratascratch.com/te...
The skills that we work on in this video include:
- Python Pandas
- Groupby & Aggregate DataFrames
- Use regexes to analyze text
- Datetime objects in Pandas
- Filtering by Conditionals
- Applying a lambda function to a data frame
If you have any questions, let me know in the comments!
If you enjoyed this video, make sure to throw it a like & subscribe for all future content :)
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Video Timeline!
0:00 - Intro & Video Overview
0:46 - Check out this Video’s Sponsor, Brilliant!
3:10 - Coding #1 (Microsoft, Easy) - Finding Updated Records
10:36 - Coding #2 (Airbnb, Easy) - Number of Bathrooms and Bedrooms
16:38 - Coding #3 (Google, Medium) - Counting Instances in Text
28:23 - Coding #4 (Meta/Facebook, Medium) - Customer Revenue in March
36:51 - Coding #5 (Amazon, Hard) - Monthly Percentage Difference
56:38 - Coding #6 (Microsoft, Hard) - Premium vs Freemium
01:10:28 - Non-Coding #1 (Visa, Easy) - Credit Card Activity
01:13:33 - Non-Coding #2 (IBM, Easy) - Outliers Detection
01:16:46 - Non-Coding #3 (Google, Medium) - Probability of Having a Sister
01:27:19 - Non-Coding #4 (Uber, Medium) - Uber Black Rides
01:36:57 - Non-Coding #5 (Capital One, Hard) - Terabyte of Data
01:46:41 - Video Conclusion & Recap
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This video was Sponsored by Brilliant

[@KeithGalli]

Thank you Brilliant for sponsoring this video! Check out brilliant.org/KeithGalli/ to get started learning STEM for free, and the first 200 people will get 20% off their annual premium subscription. Hope you all enjoyed this video :). I'm working on a bunch of new content right now so be on the lookout for another video or two in the next couple of weeks. If you have any questions about the topics covered in this or have a request for a future video, let me know here in the comments!!

[@edwardj.warden5072]

Hi @KeithGalli. I’ve got two questions to ask you. I have watched lots of your videos that I like, and learned a lot. My question is do you think that the certificate that Datacamp provides for data science is worth to earn, and would it help me to find a data science job? And, what best place, you recommend, in online to get certificate for data science that would help me to find a data science job? Thank you.

[@hardiktyagi1955]

At 37:48 I work for Amazon's RPA team, trying to make a career in data science. Last month I was appearing for an IJP and got the same question in SQL coding round. Thanks for making this Keith. Keep them coming.

[@KeithGalli]

Dang that's too funny. My hope is that this video will help people in similar situations to yours moving forward. Thanks for watching!

[@shivamburnwal7765]

Hey Hardik, can you tell me why exactly you are trying to make a career in Data Science? Is it because RPA doesn't have a good future in the industry or it is because you personally prefer the Data Science field. I am asking this question as I am also starting as a member of EXL's RPA team.

[@yogeshuttekar8542]

Glad to see you back mate. I have really learned more from your videos than attending University.

[@deepaksaikumar5178]

Hi Keith, You have been a great resource to learn Python and Data science-related skills. Thank you!

[@BOGABOOfull]

Glad you're back bro ;) love this types of vids. Love from Portugal

[@nicholasgrandizio7596]

Thank you for all the hard work you put into teaching Data Science. Your videos and others like you, provide more to the community such as myself trying to build a career in data than what University Programs provide. Your playing an important role in the future of Data Science by leading current students along the path to future industry leaders.

[@dinkinflicka157]

Yay! Another real world problem solving video. Thanks Keith. Love your content as always.

[@KeithGalli]

Glad to hear it, I appreciate your support!! :)

[@laurentreynaud4404]

Thank you so much for these data science courses!

[@danielefarotti1061]

I really like your approach in explaining things. I am currently transitioning from pure maths into data science, and I find these videos very helpful!

[@Lnd2345]

Here's a one liner chained version I've come up with for coding #6 df = ms_user_dimension.merge(ms_acc_dimension, on = 'acc_id').merge(ms_download_facts ,on ='user_id').pivot_table(index = 'date',columns = 'paying_customer',values = 'downloads',aggfunc ='sum').reset_index().query('no > yes')

[@netanelmad]

Thanks for the video! Would love to see your approach to more non-coding questions specifically :)

[@masked00000]

You're literally the best tutor I have seen, I myself am a Data Scientist but the amount of data science approaches I learn from you is incredible, I started from your channel and always wait for you to post new video, Hat's off. Love from Pakistan.

[@edwardj.warden5072]

Very helpful. Thank you Keith.

[@adeafni9544]

Thank you Keith, you're amazingg, keep it up!!!

[@arashomranpour5468]

good having you back

[@KeithGalli]

Good to be back! :)

[@niteshprajapat7918]

You are gem ❤️ the way you explain concepts are at next level 🔥🔥

[@xxxihabxxx1]

this took me a week to finish all coding questions, 10000% helped me alot to practice everything i learned in your previous pandas crash crourse. thanks

[@zanerios2776]

really love the style and format of vid, just subbed

[@KeithGalli]

Glad you liked it man! Thanks for the sub

[@ansekao4516]

Great video, please do more like that. Watching you for a long time

[@kennethstephani692]

Great video, Keith!

[@wiz8058]

Great work man!! you're always doing the best.🔥🔥🔥

[@KeithGalli]

Thank you for the support as always!!

[@troy671]

Thanks for the video. It is great to see your thinking process even though you are not an expert in pandas.

[@mekuzeeyo]

Thank you for coming back🤗

[@KeithGalli]

Happy to be back!!

[@a.5214]

amazing! we want more of this stuff 👌

[@KeithGalli]

Appreciate it! More coming soon :)

[@expat2010]

I really enjoy the real world feel of your videos. Probably now ChatGPT would be a lot faster than searching Stackoverflow or the Pandas docs for those things that one doesn't know by heart.

[@phoenixcollege6608]

makes it easy to understand watching your vid on a friday night and these are the best years of my young life

[@kumaripritika2799]

Really helpful video!

[@user-xj9re7gv5g]

It is very great. Thank You!

[@iamTHIEN013]

Hi Keith , Thank you so much for these videos, could you make more videos about power PI or Tableau, really really appreciate it .

[@udayabhaskar1495]

Thank you for this video!👍

[@bobbyg603]

Glad you're back bro!

[@KeithGalli]

thanks brother!!

[@n_12346]

Brilliant video! very helpfil

[@9eartheyes]

great video! thank you!

[@prof_albert]

That was great. Bravo and all of your videos are awesome 🌺👌💞🤩💪

[@wahaha108]

long time no see keith, welcome back 😀😀

[@ranjithraghunathan1267]

Thanks Keith

[@pratikpawar336]

great video, please make more video like this

[@DendrocnideMoroides]

yes please make more videos like this

[@iamfavoured9142]

Welcome back Keith 💃🏻💃🏻

[@mehdismaeili3743]

excellent, thanks.

[@KeithGalli]

You're welcome :)

[@phsopher]

For the fifth problem, pandas has an in-built percentage difference method (pct_change). The solution could be as follows for example: sf_transactions['year_and_month'] = sf_transactions.created_at.dt.strftime("%Y-%m") monthly_revenue = sf_transactions.groupby(["year_and_month"]).sum().reset_index() monthly_revenue['pct_change'] =(monthly_revenue.value.pct_change()*100).round(2) monthly_revenue[['year_and_month','pct_change']]

[@KeithGalli]

Oh cool, I didn't know that! Thanks for sharing :). Nice solution 🤠.

[@RahmanIITDelhi]

Hey ,Keith ..Can we access library during the solving at real time exam?

[@finnnelson5472]

TY :)

[@drakkarleon]

Yeeeeeeeeyyy!!!! i love your enthusiastic cry of success :D 26:31

[@AIdevel]

The problem lays in your use of round function you supposed to wrap the equation with round and then select the decimals 2

[@fcoatis]

Great video Keith. I just got curious how you comment a block of code?

[@kinghezzy]

Highlight and ctrl+/

[@fantasyxpress7966]

Is dsa important for data scientists too keith

[@user-zm6kj7oi3d]

you are helping a high schooler out by being back

[@KeithGalli]

More videos coming soon :)

[@user-if1dj7fy2y]

Bravo 👏 Lit 🌠 Impressive 👌 ❤ Gratitude 🥳 for your satisfactory Work 💪🚀💯💪

[@anonviewerciv]

That first one and others are SQL problems converted to pandas. I suppose that's a decent way to get basic pd questions. (28:48) 17:20 I know it's more a reference to the stock market terms, but I can't stop thinking of Fallout: New Vegas. 1:11:00 If you have the locations that's just a simple matter of putting it on a map and seeing where it clusters the most. 1:28:00 Context, context, context. Was that the only reduction?

[@konstantinpluzhnikov4862]

These stratascratch tasks could be solved in sql. The site provides this option.

[@ranjithraghunathan1267]

how can i download or copy the raw dataset for each part ?

[@vanshmalik1446]

Hey! Does anyone knows more of the data analysis pay after placement programs accepting applications all over the globe?

[@jovanjanjic9029]

In question #3 Counting Instances in Text you should add filters=re.I to account for capital letters: len(re.findall(r'\bbull\b', text, flags=re.I)))

[@jovanjanjic9029]

Great video btw!

[@MikeResurrected]

Could you actually google for help during a DS coding interview nowadays?

[@balakumar.n4891]

super

[@AIdevel]

Replace yes with 1 and no with zero and sum them

[@manphu2515]

Thanks so much for the video, learn a lot from you. And you are super cute 😍

[@konstantinpluzhnikov4862]

LifeHack: if you are short of money, but want to use a service, use vpn of relatively poor country. Result will be interesting.

[@DendrocnideMoroides]

did you ever use it? and on which website?

[@YunusFidan_]

Noice!

[@jovanjanjic9029]

Your solution for the Probability of Having a Sister question is not correct. We know for sure that the random girl must be from the [1, 2, 3, 4] part of the dataset, which amounts to 0.7. We should divide the probabilities for 1, 2, 3, 4 with 0.7, to get the probabilities that the girl is from each of these families. She theoretically can't be from families with 0 and 5 children. Essentially, you are counting in the possibilities of she being in families 0 and 5, even tough it's impossible. (In practical terms, you are needlessly being blind about the info you already have.) So the correct solution is: 0.25/0.7 x 0 + 0.2/0.7 x 0.5 + 0.15/0.7 x 0.75 + 0.1/0.7 x 0.875 = 0.42857, which is 0.43 when we round it up.

[@meujie8835]

Hi, I'm Jiemeu and I love your channel. I hope to discuss business cooperation with you.....

[@doulaishamrashikhasan8425]

you disappeared again 😢

[@KeithGalli]

My apologies! I have a video that I'm finalizing the editing for. It should be out in the next 3-4 days and then I'm going to try to be more consistent!!

[@YaIdcReportMe]

Probably not a good use of your time to watch this guy struggle with coding questions for over an hour

[@ratkillerthe]

I solved the Bathrooms/Bedrooms problem with: cols_of_interest = airbnb_search_details[['city', 'property_type', 'bathrooms', 'bedrooms']] property_results = cols_of_interest.groupby(['city','property_type']).agg( avg_bathrooms = ('bathrooms', 'mean'), avg_bedrooms = ('bedrooms', 'mean')).reset_index()