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Improving performance when calculating percentiles in Spark

Performance is a major concern when you’re working in a distributed environment with a massive amount of data. I’ve discussed Spark performance in quite a lot of detail before here and here. Today I am going to talk specifically about percentiles. Because, calculating percentiles over large distributed datasets is a mammoth task. You will likely […]

time series seasonal decomposition in python

Seasonal decomposition in timeseries analysis: additive vs multiplicative seasonality

Timeseries Decomposition is a mathematical procedure which allows us to transform our single timeseries into multiple series. These help us to extract seasonality information and trend easily. Doing this in Python is quite a simple task, I have outlined it below. However, before we get into that, we need to understand the difference between additive […]

An introduction to timeseries models (AR, MA, ARMA and ARIMA)

Timeseries forecasting is quite a big topic to cover. I’ve spoken about key terminology and exponential smoothing in this article and I’ve spoken about how we might remove timeseries outliers here. In this post, I am going to discuss the different components of the ARIMA model (AR and MA), in addition to the ARIMA model […]

Key terminology & process for timeseries analysis including exponential smoothing

Timeseries analysis is incredibly powerful but can get quite confusing. There is a lot of terminology which we need to understand before we can really progress with making a forecast. Ultimately, timeseries analysis is all about analysing and forecasting data that is indexed in equally spaced increments of time; i.e. minutes, seconds, days, weeks, months, […]

Spark

Overcoming Futures Timeout & Read Timeout errors in PySpark

This article covers a less than orthodox method for handling resource constraints in your PySpark code. Consider the below scenario. Here, we are loading data from four sources doing some joins & aggregations and producing an output. The problem is, we keep getting timeout errors because the data is just so large. After tuning the […]

MAE | RMSE | MAPE : Measures of model accuracy for data scientists

Mean Absolute Error (MAE) This simply takes the difference between the predicted value and the actual value for every prediction and takes an average of the result. However, to avoid values cancelling one another out, it takes the absolute value (which means, it makes all the values positive). Let’s consider an example. In the below, […]

Data Badass Early Preview

An early view of my new book ‘Data Badass’ is available to view using this link. It’s not yet been through thorough editing and will be added to over time but I am keen to gather some feedback. It’s a book that covers the data basics; data platforms (including Hadoop, Kafka, Flume, Hive, Spark) and […]

Using ROC Curves & AUC

This is a snippet from my upcoming book ‘Data Badass’ (pictured below): The ROC Curve & the Area Under Curve (AUC) is used for binary classification problems. The ROC curve chart looks at the True Positive Rate vs the False Positive Rate. Ideally, you want to reduce the number of false positives as much as […]

Data

An introduction to structured data modelling

This is an introductory chapter of my upcoming book ‘Data Badass’ (pictured below): Data modelling is all about designing the way that your data is going to be organized. Think about it like building a house; you wouldn’t start laying bricks, without a plan. How would you know that the end result would meet your […]

Data

An introduction to data structures for aspiring data engineers

This is an introductory chapter of my upcoming book ‘Data Badass’ (pictured below): Data Types Data types are ways to classify data. For example, integer, string and boolean. These assignments / classifications determine what kind of values we can store in our data structures (outlined below). A string, is simply a text value. An example […]

Python

Scraping COVID-19 data from websites using Beautiful Soup

This article will overview how to extract data through screen scraping from a website. Specifically, this will focus on the UK government, open data website. Scraping websites is a contentious topic – while some websites don’t mind you doing it; some really would rather you didn’t and put in measures to try and stop you. […]

Spark

Handling data skew / imbalanced partitions in Pyspark

Data Skew is a real problem in Spark. It seems like the sort of thing which should be solved automatically by the job manager but unfortunately, it isn’t. Skew is where we have a given partition which contains a huge amount more data than others – leaving one executor to process a lot of data, […]