It’s Sailing Time (Again)

Every fall I teach a course on Introduction to Data Mining. And while the course is really on statistical learning and its applications, I also venture into classification trees. For several reasons. First, I can introduce information gain and with it feature scoring and ranking. Second, classification trees are one of the first machine learning approaches co-invented by engineers (Ross Quinlan) and statisticians (Leo Breiman, Jerome Friedman, Charles J. Stone, Richard A. Olshen). And finally, because they make the base of random forests, one of the most accurate machine learning models for smaller and mid-size data sets.

Lecture on classification trees has to start with the data. Years back I have crafted a data set on sailing. Every data set has to have a story. Here is one:

Sara likes weekend sailing. Though, not under any condition. Past
twenty Wednesdays I have asked her if she will have any company, what
kind of boat she can rent, and I have checked the weather
forecast. Then, on Saturday, I wrote down if she actually went to the Sea.

Data on Sara’s sailing contains three attributes (Outlook, Company, Sailboat) and a class (Sail).

The data comes with Orange and you can get them from Data Sets widget (currently in Prototypes Add-On, but soon to be moved to core Orange). It takes time, usually two lecture hours, to go through probabilities, entropy and information gain, but at the end, the data analysis workflow we develop with students looks something like this:

And here is the classification tree:

Turns out that Sara is a social person. When the company is big, she goes sailing no matter what. When the company is smaller, she would not go sailing if the weather is bad. But when it is sunny, sailing is fun, even when being alone.

Related: Pythagorean Trees and Forests

Classification trees are not very stable classifiers. Even with small changes in the data, the trees can change substantially. This is an important concept that leads to the use of ensembles like random forests. It is also here, during my lecture, that I need to demonstrate this instability. I use Data Sampler and show a classification tree under the current sampling. Pressing on Sample Data button the tree changes every time. The workflow I use is below, but if you really want to see this in action, well, try it in Orange.

Text Analysis Workshop at Digital Humanities 2017

How do you explain text mining in 3 hours? Is it even possible? Can someone be ready to build predictive models and perform clustering in a single afternoon?

It seems so, especially when Orange is involved.

Yesterday, on August 7, we held a 3-hour workshop on text mining and text analysis for a large crowd of esteemed researchers at Digital Humanities 2017 in Montreal, Canada. Surely, after 3 hours everyone was exhausted, both the audience and the lecturers. But at the same time, everyone was also excited. The audience about the possibilities Orange offers for their future projects and the lecturers about the fantastic participants who even during the workshop were already experimenting with their own data.

The biggest challenge was presenting the inner workings of algorithms to a predominantly non-computer science crowd. Luckily, we had Tree Viewer and Nomogram to help us explain Classification Tree and Logistic Regression! Everything is much easier with vizualizations.

Classification Tree splits first by the word ‘came’, since it results in the purest split. Next it splits by ‘strange’. Since we still don’t have pure nodes, it continues to ‘bench’, which gives a satisfying result. Trees are easy to explain, but can quickly overfit the data.

Logistic Regression transforms word counts to points. The sum of points directly corresponds to class probability. Here, if you see 29 foxes in a text, you get a high probability of Animal Tales. If you don’t see any, then you get a high probability of the opposite class.

At the end, we were experimenting with explorative data analysis, where we had Hierarchical Clustering, Corpus Viewer, Image Viewer and Geo Map opened at the same time. This is how a researcher can interactively explore the dendrogram, read the documents from selected clusters, observe the corresponding images and locate them on a map.

Hierarchical Clustering, Image Viewer, Geo Map and Corpus Viewer opened at the same time create an interactive data browser.

The workshop was a nice kick-off to an exciting week full of interesting lectures and presentations at Digital Humanities 2017 conference. So much to learn and see!

Text Analysis: New Features

As always, we’ve been working hard to bring you new functionalities and improvements. Recently, we’ve released Orange version 3.4.5 and Orange3-Text version 0.2.5. We focused on the Text add-on since we are lately holding a lot of text mining workshops. The next one will be at Digital Humanities 2017 in Montreal, QC, Canada in a couple of days and we simply could not resist introducing some sexy new features.

Related: Text Preprocessing

Related: Rehaul of Text Mining Add-On

First, Orange 3.4.5 offers better support for Text add-on. What do we mean by this? Now, every core Orange widget works with Text smoothly so you can mix-and-match the widgets as you like. Before, one could not pass the output of Select Columns (data table) to Preprocess Text (corpus), but now this is no longer a problem.

Of course, one still needs to keep in mind that Corpus is a sparse data format, which does not work with some widgets by design. For example, Manifold Learning supports only t-SNE projection.

Second, we’ve introduced two new widgets, which have been long overdue. One is Sentiment Analysis, which enables basic sentiment analysis of corpora. So far it works for English and uses two nltk-supported techniques – Liu Hu and Vader. Both techniques are lexicon-based. Liu Hu computes a single normalized score of sentiment in the text (negative score for negative sentiment, positive for positive, 0 is neutral), while Vader outputs scores for each category (positive, negative, neutral) and appends a total sentiment score called a compound.

Try it with Heat Map to visualize the scores.

Yellow represent a high, positive score, while blue represent a low, negative score. Seems like Animal Tales are generally much more negative than Tales of Magic.

The second widget we’ve introduced is Import Documents. This widget enables you to import your own documents into Orange and outputs a corpus on which you can perform the analysis. The widget supports .txt, .docx, .odt, .pdf and .xml files and loads an entire folder. If the folder contains subfolders, they will be considered as class values. Here’s an example.

This is the structure of my Kennedy folder. I will load the folder with Import Documents. Observe, how Orange creates a class variable category with post-1962 and pre-1962 as class values.

Subfolders are considered as class in the category column.

Now you can perform your analysis as usual.

Finally, some widgets have cool new updates. Topic Modelling, for example, colors words by their weights – positive weights are colored green and negative red. Coloring only works with LSI, since it’s the only method that outputs both positive and negative weights.

If there are many kings in the text and no birds, then the text belongs to Topic 2. If there are many children and no foxes, then it belongs to Topic 3.

Take some time, explore these improvements and let us know if you are happy with the changes! You can also submit new feature requests to our issue tracker.

Thank you for working with Orange! 🍊