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Category: Machine Learning

Image Counts For Neural Network Training

Published 2017-12-15 by Kevin Feasel

Pete Warden shares his rule of thumb for how many images you need to train a neural network:

In the early days I would reply with the technically most correct, but also useless answer of “it depends”, but over the last couple of years I’ve realized that just having a very approximate rule of thumb is useful, so here it is for posterity:

You need 1,000 representative images for each class.

Like all models, this rule is wrong but sometimes useful. In the rest of this post I’ll cover where it came from, why it’s wrong, and what it’s still good for.

Read on to learn where the number 1000 came from and get some good hints, like flipping and rescaling images.

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Capsule Neural Networks

Published 2017-12-14 by Kevin Feasel

Saurabh Kulshrestha covers the topic of capsule neural networks:

This is the problem with Convolutional Neural Networks as well. CNN is good at detecting features, but will wrongly activate the neuron for face detection. This is because it is less effective at exploring the spatial relationships among features.

A simple CNN model can extract the features for nose, eyes and mouth correctly but will wrongly activate the neuron for the face detection. Without realizing the mis-match in spatial orientation and size, the activation for the face detection will be too high.

Read on to see how capsule networks can help solve issues with convolutional neural networks.

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Creating An Azure Chat Bot

Published 2017-12-14 by Kevin Feasel

Dustin Ryan shows how to build a QnA bot:

After you’ve created your knowledge base you can then edit and update your knowledge base. There’s a few different ways to update your knowledge.

a. Manually edit the knowledge base directly within QnAMaker.ai. You can do this by directly editing the questions by modifying the text of your knowledge base.

b. Edit the source of your knowledge base. Click the Settings tab on the left to edit the URL of your FAQs or upload a new document.

Building a bot is pretty easy, and Dustin shows you just how to do it.

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Estimating Used Car Prices

Published 2017-12-07 by Kevin Feasel

Kevin Jacobs wants to estimate the value of his car and shows how to set up a machine learning job to do this:

As you can see, I collected the brand (Peugeot 106), the type (1.0, 1.1, …), the color of the car (black, blue, …) the construction year of the car, the odometer of the car (which is the distance in kilometers (km) traveled with the car at this point in space and time), the ask price of the car (in Euro’s), the days until the MOT (Ministry of Transport test, a required periodical check-up of your car) and the horse power (HP) of the car. Feel free to use your own variables/units!

It’s an interesting example of how you can approach a real problem.

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Introduction To Neural Nets

Published 2017-12-07 by Kevin Feasel

Ben Gorman has a two-part series introducing neural networks.  First, the basics behind neural networks:

We can solve both of the above issues by adding an extra layer to our perceptron model. We’ll construct a number of base models like the one above, but then we’ll feed the output of each base model as input into another perceptron. This model is in fact a vanilla neural network. Let’s see how it might work on some examples.

Then, he digs into the mathematics of backpropagation:

Our problem is one of binary classification. That means our network could have a single output node that predicts the probability that an incoming image represents stairs. However, we’ll choose to interpret the problem as a multi-class classification problem – one where our output layer has two nodes that represent “probability of stairs” and “probability of something else”. This is unnecessary, but it will give us insight into how we could extend task for more classes. In the future, we may want to classify {“stairs pattern”, “floor pattern”, “ceiling pattern”, or “something else”}.

Our measure of success might be something like accuracy rate, but to implement backpropagation (the fitting procedure) we need to choose a convenient, differentiable loss function like cross entropy. We’ll touch on this more, below.

This is definitely a series to read after you’ve gotten your coffee.

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Training Convolutional Neural Networks On Satellite Image Data

Published 2017-12-06 by Kevin Feasel

Ahmet Taspinar builds a neural net which detects roads in satellite images:

Next we will determine the contents of each tile image, using data from the NWB Wegvakken (version September 2017). This is a file containing all of the roads of the Netherlands, which gets updated frequently. It is possible to download it in the form of a shapefile from this location.
Shapefiles contain shapes with geospatial data and are normally opened with GIS software like ArcGIS or QGIS. It is also possible to open it within Python, by using the pyshp library.

This is a pretty lengthy and interesting tutorial.  H/T Data Science Central

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Predicting Restaurant Reservations With A Neural Net

Published 2017-12-01 by Kevin Feasel

Kevin Jacobs builds a simple neural net using Pandas and sklearn:

The first thing to notice is that our values are not normalized. The number of visitors is a number and gets larger and larger. To normalize it, we simply divide it by 100, since all numbers are below 1. The same holds for the lag. Most of the lags are lower than 30. Therefore, I will divide the lag size by 30.

Notice that there are many more approaches for normalizing the data! This is just a quick normalization on the data, but feel free to use your own normalization method. My normalization process is closely related to the MinMaxScalar normalization which can be found in sklearn (scikit-learn).

With just a few lines of Python code we can create a Multi-Layer Perceptron (MLP):

Click through for the code.

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Using Keras To Predict Customer Churn

Published 2017-11-30 by Kevin Feasel

Matt Dancho has an example of building a neural net using Keras to predict customer churn:

Pro Tip: A quick test is to see if the log transformation increases the magnitude of the correlation between “TotalCharges” and “Churn”. We’ll use a few dplyr operations along with the corrr package to perform a quick correlation.

  • correlate(): Performs tidy correlations on numeric data

  • focus(): Similar to select(). Takes columns and focuses on only the rows/columns of importance.

  • fashion(): Makes the formatting aesthetically easier to read.

This is a very useful tutorial.

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Tidy Word Vectors Revisited

Published 2017-11-29 by Kevin Feasel

Julia Silge revisits her Hacker News word vectorization problem:

So hooray! We have found word vectors again, a bit faster, with clearer and easier-to-understand code. I do argue that this is a real benefit of this approach; it’s based on counting, dividing, and matrix decomposition and is thus much easier to understand and implement than anything with a neural network. And the results?

Click through to see the new method, as well as some basic analogy testing.

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