Examining Numbers in OpenRefine

Overview

Teaching: 5 min
Exercises: 5 min

Questions

• How can we convert a column from one data type to another?

Objectives

• Transform a text column into a number column.

• Identify non-numeric values in a column using facets.

Numbers

When a table is imported into OpenRefine, all columns are treated as having text values. As we saw earlier with dates, we can transform columns to other data types (e.g. date or number) using the Edit cells > Common transforms feature. Here we will experiment changing columns to numbers and see what additional capabilities that grants us.

Be sure to remove any Text filter facets you have enabled from the left panel so that we can examine our whole dataset. You can remove an existing facet by clicking the x in the upper left of that facet window.

To transform cells in the Number of Holds column to numbers, click the down arrow for that column, then Edit cells > Common transforms ... > To number. You will notice the Number of Holds values change from left-justified to right-justified, and black to green in color.

Exercise

Try Transforming the Title column to number. What happens?

Solution

Only observations that include only numerals (0-9) can be transformed to numbers. If you apply a number transformation to a column that doesn’t meet this criteria, and then click the Undo / Redo tab, you will see a step that starts with Text transform on 0 cells. This means that the data in that column was not transformed.

Click above this change in the undo stack so that this failed operation is removed from our undo history.

Numeric facet

Sometimes there are non-number values or blanks in a column which may represent errors in data entry and we want to find them. We can do that with a Numeric facet.

Exercise

1. For the Number of Holds column, edit one or two cells, replacing the numbers with text (such as abc) or blank (no number or text).
2. Use the pulldown menu to apply a numeric facet to the column you edited. The facet will appear in the left panel.
3. Notice that there are several checkboxes in this facet: Numeric, Non-numeric, Blank, and Error. Below these are counts of the number of cells in each category. You should see checks for Non-numeric and Blank if you changed some values.
4. Experiment with checking or unchecking these boxes to select subsets of your data.
5. Go to the undo stack in the Undo / Redo tab to undo these single cell edits.

Go to the numberic facet and press reset. The graph in the facet gives us a histogram of how many times each number in the column has appeared.

Play with the facet – at the far right of the histogram are the titles with the most number of requests for the users of a branch for a specific week. What was the item that had the most requests at a branch for a week?

When done examining the numeric data, remove this facet by clicking the x in the upper left corner of its panel.

Key Points

• OpenRefine also provides ways to get overviews of numerical data.