Filtering and Sorting with OpenRefine

Last updated on 2023-05-09 | Edit this page

Estimated time 35 minutes

Overview

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.

Filtering

Sometimes you want to view and work only with a subset of data or apply an operation only to a subset. You can do this by applying various filters to your data.

Including/excluding data entries on facets

One way to filter down our data is to use the include or exclude buttons on the entries in a text facet. If you still have your text facet for scientificName, you can use it. If you’ve closed that facet, recreate it by selecting Facet > Text facet on the scientificName column.

  1. In the text facet, hover over one of the names, e.g. Baiomys taylori. Notice that when you hover over it, there are buttons to the right for edit and include.
  2. Whilst hovering over Baiomys taylori, move to the right and click the include option. This will include this species, as signified by the name of the species changing from blue to orange, and new options of edit and exclude will be presented. Note that in the top of the page, “33 matching rows” is now displayed instead of “790 rows”.
  3. You can include other species in your current filter - e.g. click on Chaetodipus baileyi in the same way to include it in the filter.
  4. Alternatively, you can click the name of the species to include it in the filter instead of clicking the include/exclude buttons. This will include the selected species and exclude all others options in a single step, which can be useful.
  5. Click include and exclude on the other species and notice how the entries appear and disappear from the data table to the right.

Click on Reset at the top-right of the facet before continuing to the next step.

Text filters

One way to filter data is to create a text filter on a column. Close all facets you may have created previously and reinstate the text facet on the scientificName column.

  1. Click the down arrow next to scientificName > Text filter. A scientificName filter will appear on the left margin below the text facet.

  2. Type in bai into the text box in the filter and press return. At the top of the page it will report that, out of the 790 rows in the raw data, there are 35 rows in which the text has been found within the scientificName column (and these rows will be selected for the subsequent steps).

OpenRefine filtering example
  1. Near the top of the screen, change Show: to 50. This way, you will see all the matching rows in a single page.

Exercise

  1. What scientific names are selected by this text filter?
  2. How would you restrict the filter to one of the species selected?
  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:
  • Check the case sensitive box within the scientificName facet. Once you do this, you will see that using the upper-case Bai will only > > return Baiomys taylori, while using lower-case bai will only return Chaetodipus baileyi.
  • You could include more letters in your filter (i.e. typing baio will exclusively return Baiomys taylori, while bail will only return Chaetodipus baileyi).

Filters vs. facets

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

Important: Make sure both species (Baiomys taylori and Chaetodipus baileyi) are included in your filtered dataset before continuing with the rest of the exercises.

Sort

Sorting data is a useful practice for detecting outliers in data - potential errors and blanks will sort to the top or the bottom of your data.

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?

In the mo column, select Sort... > numbers and select smallest first. The months are listed from 1 (for January) through 12 (December).

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:

  • Sort > Sort... - This option enables you to modify your original sort.

  • Sort > Reverse - This option allows you to reverse the order of the sort.

  • Sort > Remove sort - This option allows you to undo your sort.

Exercise

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

In the plot column, select Sort... > numbers and select smallest first. The years represented include 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?
  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 also sort by days within each month. Click on the dy column then Sort > numbers. Your data should now be in chronological order.

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.

Keypoints

  • OpenRefine provides various ways to sort and filter data without affecting the raw data.