Clustering

Overview

Teaching: 10 min
Exercises: 10 min

Questions

• What is Clustering in OpenRefine and when would you use it?

• How does clustering work in OpenRefine?

Objectives

• Explain what clustering is in OpenRefine

• Use clustering to identify and fix replace varying forms of the same data with a single consistent value

Clustering

The Cluster function groups together similar, but inconsistent values in a given column and lets you merge these inconsistent values into a single value you choose.

This is very effective where you have data with minor variations in data values, e.g. names of people, organisations, places, classification terms.

To use the ‘Cluster’ function, click on the Edit Cells menu option in the relevant column and choose Cluster and edit...

The ‘Clusters’ are created automatically according to an algorithm. OpenRefine supports a number of different clustering algorithms - some experimentation may be required to see which clustering algorithm works best with any particular set of data, and you may find that using different algorithms highlights different clusters.

For more information on the methods used to create Clusters, see https://github.com/OpenRefine/OpenRefine/wiki/Clustering-In-Depth

For each cluster, you have the option of ‘merging’ the values together - that is, replace the various inconsistent values with a single consistent value. By default, OpenRefine uses the most common value in the cluster as the new value, but you can select another value by clicking the value itself, or you can simply type the desired value into the ‘New Cell Value’ box.

Use Clustering to clean up author data

1. Split out the author names into individual cells using Edit cells -> Split multi-valued cells, using the pipe ( | ) character as the separator
2. Choose Edit cells -> Cluster and edit from the ‘author’ column.
3. Using the key collision method with the fingerprint Keying Function, work through the clusters of values, merging them to a single value where appropriate
4. Try changing the clustering method being used - which ones work well?

Key Points

• Clustering is a way of finding variant forms of the same piece of data within a dataset (e.g. different spellings of a name)

• There are a number of different Clustering algorithms that work in different ways and will produce different results

• The best clustering algorithm to use will depend on the data

• Using clustering you can replace varying forms of the same data with a single consistent value