Filtering and Sorting with OpenRefine

Overview

Teaching: 10 min
Exercises: 10 min
Questions
  • How can we select only a subset of our data to work with?

  • How can we sort our data?

Objectives
  • Employ text filter or include/exclude to filter to a subset of rows.

  • Sort tables by a column.

  • Sort tables by multiple columns.

Lesson

Filtering

There are many entries in our data table. We can filter it to work on a subset of the data in the list for the next set of operations. Please ensure you perform this step to save time during the class.

  1. Click the down arrow next to scientificName > Text filter. A scientificName facet will appear on the left margin.
  2. Type in bai and press return. There are 48 matching rows of the original 35549 rows (and these rows are selected for the subsequent steps).
  3. At the top, change the view to Show 50 rows. This way you will see all the matching rows.

Exercise

  1. What scientific names (genus and species) are selected by this procedure?
  2. How would you restrict this to one of the species selected?

Solution

  1. Do Facet > Text facet on the scientificName column after filtering. This will show that two names match your filter criteria. They are Baiomys taylori and Chaetodipus baileyi.
  2. To restrict to only one of these two species, you could make the search case sensitive or you could split the scientificName column into species and genus before filtering or you could include more letters in your filter.

Excluding entries

In addition to the solutions included above, another way to narrow our filter is to include and/or exclude entries in a facet. If you still have your facet for scientificName, you can use it, or use drop-down menu > Facet > Text facet to create a new facet. Only the entries with names that agree with your Text filter will be included in this facet.

Faceting and filtering look very similar. A good distinction is that faceting gives you an overview description of all of the data that is currently selected, while filtering allows you to select a subset of your data for analysis.

Exercise

Use include / exclude to select only entries from one of these two species.

Solution

  1. In the facet (left margin), click on one of the names, such as Baiomys taylori. Notice that when you click on the name, or hover over it, there are entries to the right for edit and include.
  2. Click include. This will explicitly include this species, and exclude others that are not expicitly included. Notice that the option now changes to exclude.
  3. Click include and exclude on the other species (Chaetodipus baileyi) and notice how the two entries appear and disappear from the table.

Important: Select both species for your filtered dataset before continuing with the rest of the exercises.

Sort

You can sort the data in a column by using the drop-down menu available in that column. There you can sort by text, numbers, dates or booleans (TRUE or FALSE values). You can also specify what order to put Blanks and Errors in the sorted results.

If this is your first time sorting this table, then the drop-down menu for the selected column shows Sort.... Select what you would like to sort by (such as numbers). Additional options will then appear for you to fine-tune your sorting.

Exercise

Sort by month. How can you ensure that months are in order?

If you try to re-sort a column that you have already used, the drop-down menu changes slightly, to > Sort without the ..., to remind you that you have already used this column. It will give you additional options:

Exercise

Sort the data by plot. What year(s) were observations recorded for plot 1 in this filtered dataset.

Solution

In the plot column, select Sort... > numbers and select smallest first. The years represented are 1990 and 1995.

Sorting by multiple columns.

You can sort by multiple columns by performing sort on additional columns. The sort will depend on the order in which you select columns to sort. To restart the sorting process with a particular column, check the sort by this column alone box in the Sort pop-up menu.

Exercise

You might like to look for trends in your data by month of collection across years.

  1. How do you sort your data by month?
  2. How would you do this differently if you were instead trying to see all of your entries in chronological order?

Solution

  1. For the mo column, click on Sort... and then numbers. This will group all entries made in, for example, January, together, regardless of the year that entry was collected.
  2. For the yr column, click on Sort > Sort... > numbers and select sort by this column alone. This will undo the sorting by month step. Once you’ve sorted by yr you can then apply another sorting step to sort by month within year. To do this for the mo column, click on Sort > numbers but do not select sort by this column alone. To ensure that all entries are shown chronologically, you will need to add a third sorting step by day within month.

If you go back to one of the already sorted columns and select > Sort > Remove sort, that column is removed from your multiple sort. If it is the only column sorted, then data reverts to its original order.

Exercise

Sort by year, month and day in some order. Be creative: try sorting as numbers or text, and in reverse order (largest to smallest or z to a).

Use > Sort > Remove sort to remove the sort on the second of three columns. Notice how that changes the order.

Key Points

  • OpenRefine provides a way to sort and filter data without affecting the raw data.