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Category: Data Science

The Elitist Shuffle And Recommenders

Published 2018-05-15 by Kevin Feasel

Rodrigo Agundez shows us a way of displaying fresh recommendations without retraining the recommender system:

Suppose you have 10,000 items in total that can be recommended to your user, you run the recommendation system over all the items and those 10,000 items get ranked in order of relevance of the content.

The application shows 5 items on the entry screen. The first time the user opens the application after the re-scoring process the top 5 ranked items are shown. It is decided that from now on (based on user control groups, investigation, AB testing, etc.) until the next re-scoring process the entry screen should not be the same every time and remain relevant for the user.

Based on an investigation from the data scientist it turns out that somewhat relevant items appear until item 100. Then the idea is to somehow shuffle those 100 items such that the top 5 items shown are still relevant but not the same.

Click through for an example in Python and how it compares favorably to a couple other shuffling algorithms.

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Building A Neural Network With TensorFlow

Published 2018-05-11 by Kevin Feasel

Julien Heiduk gives us an example of building a neural network with TensorFlow:

To use Tensorflow we need to transform our data (features) in a special format. As a reminder, we have just the continuous features. So the first function used is: tf.contrib.layers.real_valued_column. The others cells allowed to us to create a train set and test set with our training dataset. The sampling is not the most relevant but it is not the goal of this article. So be careful! The sample 67-33 is not the rule!

It’s probably an indicator that I’m a casual, but I prefer to use Keras as an abstraction layer rather than working directly with TensorFlow.

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Scientific Debt

Published 2018-05-11 by Kevin Feasel

David Robinson gives us the data science analog to technical debt:

In my new job as Chief Data Scientist at DataCamp, I’ve been thinking about the role of data science within a business, and discussing this with other professionals in the field. On a panel earlier this year, I realized that data scientists have a rough equivalent to this concept: “scientific debt.”

Scientific debt is when a team takes shortcuts in data analysis, experimental practices, and monitoring that could have long-term negative consequences. When you hear a statement like:

  • “We don’t have enough time to run a randomized test, let’s launch it”
  • “To a first approximation this effect is probably linear”
  • “This could be a confounding factor, but we’ll look into that later”
  • “It’s directionally accurate at least”

you’re hearing a little scientific debt being “borrowed”.

Read the whole thing.  I strongly agree with the premise.

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Machine Learning From Kafka

Published 2018-05-10 by Kevin Feasel

Kai Waehner has a post covering a recent talk he did on using Kafka as a data source for neural networks:

This talk shows how to build Machine Learning models at extreme scale and how to productionize the built models in mission-critical real time applications by leveraging open source components in the public cloud. The session discusses the relation between TensorFlow and the Apache Kafka ecosystem – and why this is a great fit for machine learning at extreme scale.

The Machine Learning architecture includes: Kafka Connect for continuous high volume data ingestion into the public cloud, TensorFlow leveraging Deep Learning algorithms to build an analytic model on powerful GPUs, Kafka Streams for model deployment and inference in real time, and KSQL for real time analytics of predictions, alerts and model accuracy.

Sensor analytics for predictive alerting in real time is used as real world example from Internet of Things scenarios. A live demo shows the out-of-the-box integration and dynamic scalability of these components on Google Cloud.

Check out the slide deck as well for more details.

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Overfitting With Polynomial Regression

Published 2018-05-10 by Kevin Feasel

Vincent Granville shows us a few problems with polynomial regression:

Even if the function to be estimated is very smooth, due to machine precision, only the first three or four coefficients can be accurately computed. With infinite precision, all coefficients would be correctly computed without over-fitting. We first explore this problem from a mathematical point of view in the next section, then provide recommendations for practical model implementations in the last section.

This is also a good read for professionals with a math background interested in learning more about data science, as we start with some simple math, then discuss how it relates to data science. Also, this is an original article, not something you will learn in college classes or data camps, and it even features the solution to a linear regression involving an infinite number of variables.

Granville’s point that overfitting is a relatively small concern is rather interesting.  But the advice to avoid polynomial regression is generally pretty solid.

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Relationships Between Numerical Features

Published 2018-05-07 by Kevin Feasel

Stacia Varga continues her exploratory data analysis series using hockey data:

Let’s start with something easy and understandable to analyze. If I put age on the horizontal axis and weight on the vertical axis. It’s a common practice to put an explanatory variable on the horizontal axis and a response variable on the vertical axis. In other words, I’m looking to see how an increase in age (explanation) affects – or not – weight (response) for all the hockey players in the current season, regardless of team.

If I put age on the horizontal axis – does this explain weight? Sort of – the combinations of age and weight have some groupings. It almost appears that there is a greater number of younger, heavier players than older, heavier players, but it’s hard to tell here how the age/weight combinations are distributed because I can’t see all the individual points.

Read the whole thing, while keeping in mind that correlation does not imply causation.

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Toward Interpretable Machine Learning

Published 2018-05-02 by Kevin Feasel

Cristoph Molnar shows off a couple of R packages which help interpret ML models:

Machine learning models repeatedly outperform interpretable, parametric models like the linear regression model. The gains in performance have a price: The models operate as black boxes which are not interpretable.

Fortunately, there are many methods that can make machine learning models interpretable. The R package imlprovides tools for analysing any black box machine learning model:

  • Feature importance: Which were the most important features?
  • Feature effects: How does a feature influence the prediction? (Partial dependence plots and individual conditional expectation curves)
  • Explanations for single predictions: How did the feature values of a single data point affect its prediction? (LIME and Shapley value)
  • Surrogate trees: Can we approximate the underlying black box model with a short decision tree?
  • The iml package works for any classification and regression machine learning model: random forests, linear models, neural networks, xgboost, etc.

This is a must-read if you’re getting into model-building. H/T R-Bloggers

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Tidy Anomaly Detection With Anomalize

Published 2018-04-18 by Kevin Feasel

Abdul Majed Raja walks us through an example using the anomalize package:

One of the important things to do with Time Series data before starting with Time Series forecasting or Modelling is Time Series Decomposition where the Time series data is decomposed into Seasonal, Trend and remainder components. anomalize has got a function time_decompose() to perform the same. Once the components are decomposed, anomalize can detect and flag anomalies in the decomposed data of the reminder component which then could be visualized with plot_anomaly_decomposition() .

btc_ts %>% time_decompose(Price, method = "stl", frequency = "auto", trend = "auto") %>% anomalize(remainder, method = "gesd", alpha = 0.05, max_anoms = 0.2) %>% plot_anomaly_decomposition()

As you can see from the above code, the decomposition happens based on ‘stl’ method which is the common method of time series decomposition but if you have been using Twitter’s AnomalyDetection, then the same can be implemented in anomalize by combining time_decompose(method = “twitter”) with anomalize(method = "gesd"). Also the ‘stl’ method of decomposition can also be combined with anomalize(method = "iqr") for a different IQR based anomaly detection.

Read on to see what else you can do with anomalize.

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Uploading Data Sets To Azure ML From R

Published 2018-04-18 by Kevin Feasel

Leila Etaati continues her series on the Azure ML R package by showing how to upload a data set:

There is a function in AzureML package name “workspace” that creates a reference to an AzureML Studio workspace by getting the authentication token and workspace id as below:

to work with other AzureML packages you need to pass this object to them.

for instance for exploring the all experiments in Azure ML there is a function name “experiments” that gets the “ws” object as input to connect the desire azure ml environment and also a filter.

Click through for  more.

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The Theory Behind ARIMA

Published 2018-04-17 by Kevin Feasel

Bidyut Ghosh explains how the ARIMA forecasting method works:

The earlier models of time series are based on the assumptions that the time series variable is stationary (at least in the weak sense).

But in practical, most of the time series variables will be non-stationary in nature and they are intergrated series.

This implies that you need to take either the first or second difference of the non-stationary time series to convert them into stationary.

Bidyut ends with a little bit of implementation in R, but I’d guess that’ll be the focus of part 2.

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