d3.scaleOrdinal()

The **d3.scaleOrdinal()** function creates an ordinal scale with a defined domain (input values) and range (output values). If no values are provided:

• The domain defaults to an empty array.
• The range defaults to a set of categorical colours (d3.schemeCategory10).

Ordinal scales are primarily used for names and categorical data with a distinct set of values (e.g., categories, colours, or labels). The output values can be strings, numbers, or other types. The scale maps a discrete set of input values (the domain) to corresponding output values (the range). The order of the data is significant.

Syntax

d3.scaleOrdinal([[domain, ]range]);

• domain: The input values to be mapped, defining the minimum and maximum values for the scale.
• range: The output values that correspond to the domain. Each value in the domain matches a value in the range.

Example

The following code example demonstrates how to map discrete categories (race positions) to specific values (runner’s finish times) using d3.scaleOrdinal():

const positionScale = d3
  .scaleOrdinal()
  .domain(['First', 'Second', 'Third'])
  .range([5.33, 5.45, 6.03]);