Yesterday I had an interview for the position of a software engineer, and it included a live coding challenge. I was not able to solve the problem during the interview, but luckily I was allowed to take it home as an assignment. When it’s solved, I looked back and I think I learnt some lessons from the interview. The most difficult thing during the interview always is to keep myself calm, but apart from it I wish I have done following things (well maybe I already did them if I was cooler).

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  1. Make sure you understand the problem by giving…

A right question is also an answer.

Aggregation is the process of performing calculations over a set of data, normally to gain its statistical figures. Splitting data into groups is a necessary step if you want to aggregate data by certain criteria, not the whole data set. This article talks about AGGREGATE FUNCTIONS and WINDOW FUNCTIONS, two main approaches to aggregate data in SQL, through an explanation section followed by a practical section with the Pokemon dataset. All technical points are based on PostgreSQL engine.

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Ok we have two methods here. So when should we use which?


I always see data manipulation as Lego games — understanding small pieces will help you create your desired models!

Aggregation is a process of collecting/splitting data based on some criteria (1) and then applying a statistical method on them so that each group will be presented as a number (2). While (1) identifies the data scope, (2) does the mathematical stuff. This article is going to explain these steps in Pandas, one of the most popular library to manipulate data in Python.

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(1) — It’s all about data

There is no much of work in this step if we want to aggregate the whole data or…


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