Spreadsheets are all about detailed data and its manipulation. Sometimes, though, you need a summary for gathering general impressions and discerning trends. That is where conditional formatting becomes useful in LibreOffice Calc – as a graphical summary for interpreting general trends in data at a glance, rather than studying the figures closely.

Contrary to first impressions, Conditional Formatting in Calc shares only part of its name with Conditional Fields or Conditional Styles in Writer. All the three features have in common is that their appearance changes depending on context. In the case of conditional formatting, for instance, the format changes when the content of the involved cells changes.

Conditional formatting is an extension of the idea of sparklines, a concept named and popularized by data visualization theorist Edward Tufte, who devoted 20 pages to the concept in his book, Beautiful Evidence [1]. Sparklines are small line graphs that fit on a line of text or in a single spreadsheet cell. They contain no figures, but from their shape, you can see the general trends in the data they map.

According to Tufte, the advantages of sparklines [2] are that they:

… vastly increase the amount of data within our eyespan and intensify statistical graphics up to the everyday routine capabilities of the human eye-brain system for reasoning about visual evidence, seeing distinctions, and making comparisons. And data graphics are no longer a special occasion in a separate place with a frame on some slide with a label "Fig. 17-B" …. Providing a straightforward and contextual look at intense evidence, sparkline graphics give us some chance to be approximately right rather than exactly wrong.

Excel supports sparklines, but Calc does not, although some proof-of-concept macros were circulating a few years ago. However, conditional formatting offers several alternatives to sparklines that provide the same visual advantages while adding some complexity to the basic idea.

How Conditional Formatting Works

Conditional formatting in Calc automatically changes the appearance of selected cells. The automatic format can be the application of a cell style or of an indicator that visually presents data in much the same way as a graph or a chart.

To use Calc's conditional formatting, select the cells to work with, then click Format | Conditional Formatting | Condition, and select an item from the submenu. All types of conditional formatting can be configured from Condition. The Color Scale and Data Bar menu items are shortcuts to options available under Condition. If necessary, you can edit the range of cells affected at the bottom of the Conditions window (Figure 1).

Figure 1: The Conditional Formatting window sets the kind of information to be indicated by the formatting.

The Conditions pane has three fields. From left to right, they are:

• The general condition.
• The filter to refine the condition.
• The numerical value that must be present to activate the conditional formatting.

Below these three fields, you have the option to select a cell style.

By changing the general condition, you can choose from the following types of conditional formatting:

• Cell value is: Applies the selected cell style when the numerical value is met. This type of formatting is useful for emphasizing target values in a range of cells. It cannot be used for cells formatted for text.
• Formula is: Applies the selected cell style to cells in which the designated formula is used. The formula is typically one that viewers of the sheet want to find easily.
• Date is: Applies the selected cell style to cells in which the designated filter is used, from Today to Last Week. This type is especially useful for locating recent information.
• All Cells | Color Scale (2 entries): Creates a gradient of two colors. The fields refer not to formulas, but to target values. The color scale is especially useful for showing high and low values in a range of cells at a glance (Figure 2).
• All Cells | Color Scale (3 entries): Like a color scale for two entries, except that a third target value is added, often a midpoint using the value Percent.
• All Cells | Data Bar: A gradient that creates a graph-like representation, typically showing how far a cell value is above or below a designated norm (Figure 3).
• All Cells | Icon Set: Adds a set of icons to summarize the contents of cells (Figure 4). Available icons include arrows, flags, checkmarks, bar graphs, emoticons, and quartered circles. Each icon set has three or four icons, with each depicting a different state. For example, traffic light icons or emoticons might designate if the results were above, below, or equal to projections.

Figure 2: A color scale, with yellow indicating the lowest value and cyan the highest. Mid-range values are different shades of green.

Figure 3: A data bar in which high values are indicated by more blue in a cell.

Figure 4: An icon set annotates results. Here, emoticons indicate that two results were neutral, and two were better than neutral.

Once you have set conditional formatting, you can select Manage from the submenu to see a summary of the instances of Conditional Formats and Edit the selections (Figure 5). You might also want to add a caption to the formatted cells to explain what is being displayed.

Figure 5: Click Manage in the Conditional submenu to Add, Edit, or Remove conditional formatting.

Adding a Sparkline

If you want to use a sparkline, you can create one manually with the following procedure:

1. Highlight the range of cells for the sparkline.
2. Select Insert | Object | Chart.
3. Create a Line graph. Use the Lines Only subtype or, if you want to emphasize the points on the graph, the Points and Lines subtype.
4. Remove each element of the chart except the line by deleting it or setting it to the same color as the background (usually white).
5. Select the chart and drag it while pressing the Shift key, so it changes size without distortion (Figure 6).

6. Position the line graph by the range of cells it represents.

   Figure 6: You can edit a chart, then shrink it down to create a sparkline.

The sparkline will update if you click it or save and reopen the spreadsheet after changing one or more figures in the range of cells.

New Dimensions to Spreadsheets

Both conditional formatting and sparklines are relatively new concepts. So far as anyone can tell, they appear to be less than 20 years old. As the workaround for sparklines in Calc indicates, they are extensions of charts and graphs, except at a higher level and with less detail. Also, unlike charts and graphs, they are integrated with the data they represent.

Think of them as the graphical equivalent of captions – an annotation that helps you make sense of your data. Even if you do not use sparklines or conditional formatting when you first design a spreadsheet, you might decide to add them later, especially in a spreadsheet that has a long, active lifetime.