Problem

A conditional format is a format in Excel that is applied to a cell if a specified condition is met. ExcelWriter’s ExcelApplication object also provides the ability to create conditional formats with the ConditionalFormat object.

These are some tips for getting started with conditional formatting in ExcelWriter.

Solution

Background

The ConditionalFormat object contains up to three Condition objects, which represent the condition that determines if the format is applied, and a Range object, which represents the cells to which the format will be applied.

The condition stores a ComparisonType, which indicates whether the cell values will be compared to one or two other values, or if a particular formula will be evaluated for each cell. The condition also stores a Style object that defines the formatting to be applied.

This example will show how to use a formula evaluation conditional format to apply a red font color if a cell value in a row of cells is less than the average of cell values across that row.

Note: This is equivalent to creating a conditional format in Excel with the option to ‘Use a formula to determine which cells to format’.

Defining the Formulas

The formula being evaluated to determine which cells to format is no different from the formula that would be used in Excel. If the formula evaluates to TRUE, the format will be applied to the cell.

In this example, there is a row of integer values. The conditional format should be applied if any one of those values is less than the average of the values. An example of this formula would be:

=(A3 < AVERAGE($A$3:$G$3))

Note: The reference to A3 is relative and will change for each cell in the range that the conditional format is applied to. $A$3:$G$3 is an absolute reference, and will not update for the cells in the range.

The other formula needed is the formula to define the range of cells that the conditional format will be applied to. In this case, the range formula is for cells A3 to G3 on Sheet1:

“=Sheet1!A3:G3”

For more information about defining formulas for ranges, please refer to this post.

Creating the Conditonal Format

To create and apply a conditional format with ExcelWriter:

1. Create a ConditionalFormat with Worksheet.CreateConditionalFormat
2. Create a Condition using the Excel evaluation formula in ConditionalFormat.CreateCondition
3. Define the conditional format Style
4. Define a Range to apply the conditional format to
5. Apply the ConditionalFormat to the Range

Code snippet:

//Create a conditional format
ConditionalFormat cf = wb.CreateConditionalFormat();

//Create the condition to be evaluated when determining which cells to format
Condition cond = cf.CreateCondition(Condition.Comparison.FormulaEvaluation, "=(A3 < AVERAGE($A$3:$G$3))");

//The conditional format will apply a red font color
cond.Style.Font.Color = wb.Palette.GetClosestColor(128, 0, 0);

//Creates a range and applies the conditional format to the range
Range cond_range = wb.CreateRange("=Sheet1!A3:G3");
cond_range.SetConditionalFormat(cf);

Adding Conditions to the Conditional Format

Since a ConditionalFormat object can hold up to 3 Condition objects, up to 3 different conditional format styles and evaluation rules can be applied for a single conditional format. For example, any cell values in A3:G3 that are over 100 should have a bold, green font.

Create two conditions instead of one:

Condition cond1 = cf.CreateCondition(Condition.Comparison.FormulaEvaluation, "=(A3 < AVERAGE($A$3:$G$3))");

Condition cond2 = cf.CreateCondition(Condition.Comparison.FormulaEvaluation,"=(A3 > 100");
Define styles for both of the conditions:

cond1.Style.Font.Color = wb.Palette.GetClosestColor(128, 0, 0);
cond2.Style.Font.Color = wb.Palette.GetClosestColor(0, 128, 0);
cond2.Style.Font.Bold = true;

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