Hanjo Odendaal explains clustering techniques using Pokemon:

To collect the data on all the first generation pokemon, I employ Hadley Wickam’s rvest package. I find it very intuitive and can handle all of my needs in collecting and extracting the data from a pokemon wiki. I will grab all the Pokemon up until to Gen II, which constitutes 251 individuals. I did find the website structure a bit of a pain as each pokemon had very different looking web pages. But, with some manual hacking, I eventually got the data in a nice format.

This probably means a lot more to you if you grew up in front of a Game Boy, but there’s some good technique in here regardless.

Alex Woodie notes the increased popularity of Python for data analysis:

According to the results of the 2016 survey, R is the preferred tool for 42% of analytics professionals, followed by SAS at 39% and Python at 20%. While Python’s placing may at first appear to relegate the language to Bronze Medal status, it’s the delta here that really matters.

It’s interesting to see the breakdowns of who uses which language, comparing across industry, education, work experience, and geographic lines.

Sergey Bryl has an introductory-level post on what Markov chains are and how they work:

Using Markov chains allow us to switch from heuristic models to probabilistic ones. We can represent every customer journey (sequence of channels/touchpoints) as a chain in a directed Markov graph where each vertex is a possible state (channel/touchpoint) and the edges represent the probability of transition between the states (including conversion.) By computing the model and estimating transition probabilities we can attribute every channel/touchpoint.

Let’s start with a simple example of the first-order or “memory-free” Markov graph for better understanding the concept. It is called “memory-free” because the probability of reaching one state depends only on the previous state visited.

Markov chains are great for behavior prediction and sentence formation. This is part one of a series I will eagerly anticipate. H/T R Bloggers.

Bob Horton explains ROC curves and shows how to create them in R:

ROC curves are commonly used to characterize the sensitivity/specificity tradeoffs for a binary classifier. Most machine learning classifiers produce real-valued scores that correspond with the strength of the prediction that a given case is positive. Turning these real-valued scores into yes or no predictions requires setting a threshold; cases with scores above the threshold are classified as positive, and cases with scores below the threshold are predicted to be negative. Different threshold values give different levels of sensitivity and specificity. A high threshold is more conservative about labelling a case as positive; this makes it less likely to produce false positive results but more likely to miss cases that are in fact positive (lower rate of true positives). A low threshold produces positive labels more liberally, so it is less specific (more false positives) but also more sensitive (more true positives). The ROC curve plots true positive rate against false positive rate, giving a picture of the whole spectrum of such tradeoffs.

ROC curves are one of the primary techniques for figuring out if a binary classifier “works.”

I have a long, long post on figuring out how far SQL Saturday attendees tend to drive:

Before I begin, allow me to perform the data science Airing of Grievances. This is an important part of data analysis which most people gloss over, instead jumping right into the “clean up the dirty data” phase. But no, let’s revel in its filth for just a few moments.

Despite my protestations and complaints, I think there are some reasonable conclusions. If you need to look like you’re working for a couple of hours (or at least want to play around a bit with SQL and R), this is the post for you.

Stacia Varga has a follow-up to her Gentle Introduction to Data Analytics:

Q: How is data analytics on SAS different from R support for SQL2016?A: I’ve not used SAS (although I did go to their campus to teach MDX to their engineers once upon a time… beautiful campus!), so I can’t say with any specificity. SAS also has multiple products so it would be difficult to describe differences. In general – and please understand there may be something new in SAS that I don’t know about – I think the difference is that R in SQL 2016 allows you to run functions on data inside the database, thereby leveraging database resources and also server resources for parallelization. I’d love to get input from readers to expand on this topic.

I can confirm that SAS has a beautiful campus.

Jesse Clark explains the traveling salesman problem:

One of the canonical questions in operations is the traveling salesman problem (TSP). In its simplest form, we have a busy salesperson who must visit a set number of locations once. Time is money, so the salesperson wants to choose a route that minimizes the total distance traveled. It is not so hard to imagine these path optimization problems occurring within warehouses where people (‘pickers’) need to navigate aisles and fill orders as they go.

The Traveling Salesman Problem is a computer science classic and acts as a classic graph optimization problem. Check this post out for more details.

Mala Mahadevan looks at calculating range, variance, and standard deviation in R and T-SQL:

The first and most common measure of dispersion is called ‘

Range‘. The range is just the difference between the maximum and minimum values in the dataset. It tells you how much gap there is between the two and therefore how wide the dataset is in terms of its values. It is however, quite misleading when you have outliers in the data. If you have one value that is very large or very small that can skew the Range and does not really mean you have values spanning the minimum to the maximum.To lower this kind of an issue with outliers – a second variation of the range called

Inter-Quartile Range, orIQRis used. The IQR is calculated by dividing the dataset into 4 equal parts after sorting the said value in ascending order. For the first and third part, the maximum values are taken and then subtracted from each other. The IQR ensures that you are looking at top and near-bottom ranges and therefore the value it gives is probably spanning the range.

Just like her previous post, this one also includes an example built for SQL Server R Services.

Vik Paruchuri walks through exploratory data analysis using New York City schools data:

Heatmaps are good for mapping out gradients, but we’ll want something with more structure to plot out differences in SAT score across the city. School districts are a good way to visualize this information, as each district has its own administration. New York City has several dozen school districts, and each district is a small geographic area.

We can compute SAT score by school district, then plot this out on a map. In the below code, we’ll:

Group full by school district.

Compute the average of each column for each school district.

Convert the school_dist field to remove leading 0s, so we can match our geograpghic district data.

Also check out part 1 if you missed it.

Clustering is the task of assigning entities into groups based on similarities among those entities. The goal is to construct clusters in such a way that entities in one cluster are more closely related, i.e. similar to each other than entities in other clusters. As opposed to classification problems where the goal is to learn based on examples, clustering involves learning based on observation. For this reason, it is a form of unsupervised learning task.

There are many different clustering algorithms and a central notion in all of those is the definition of ’similarity’ between the entities that are being grouped. Different clustering algorithms may have different ways of measuring the similarity. In many clustering algorithms, another common notion is the so-called cluster center, which is a basis to represent the cluster. For example, in K-means clustering algorithm, the cluster center is the arithmetic mean position of all the points in that cluster.

This is a fairly lengthy article but if you want to get into machine learning with Spark, it’s a good one.

Kevin Feasel

2016-08-23

Data Science, R, Visualization