View Source Contex.CategoryColourScale (ContEx v0.5.0)
Maps categories to colours.
The Contex.CategoryColourScale maps categories to a colour palette. It is used, for example, to calculate
the fill colours for Contex.BarChart, or to calculate the colours for series in Contex.PointPlot.
Internally it is a very simple map with some convenience methods to handle duplicated data inputs, cycle through colours etc.
The mapping is done on a first identified, first matched basis from the provided dataset. So, for example,
if you have a colour palette of ["ff0000", "00ff00", "0000ff"] (aka red, green, blue), the mapping
for a dataset would be as follows:
| X | Y | Category | Mapped Colour |
|---|---|---|---|
| 0 | 0 | Turtle | red |
| 1 | 1 | Turtle | red |
| 0 | 1 | Camel | green |
| 2 | 1 | Brontosaurus | blue |
| 3 | 4 | Turtle | red |
| 5 | 5 | Brontosaurus | blue |
| 6 | 7 | Hippopotamus | red ← NOTE - if you run out of colours, they will cycle |
Tn use, the CategoryColourScale is created with a list of values to map to colours and optionally a colour
palette. If using with a Contex.Dataset, it would be initialised like this:
dataset = Dataset.new(data, ["X", "Y", "Category"])
colour_scale
= dataset
|> Dataset.unique_values("Category")
|> CategoryColourScale(["ff0000", "00ff00", "0000ff"])Then it can be used to look up colours for values as needed:
fill_colour = CategoryColourScale.colour_for_value(colour_scale, "Brontosaurus") // returns "0000ff"There are a number of built-in colour palettes - see colour_palette(), but you can supply your own by
providing a list of strings representing hex code of the colour as per CSS colour hex codes, but without the #. For example:
scale = CategoryColourScale.set_palette(scale, ["fbb4ae", "b3cde3", "ccebc5"])Link to this section Summary
Functions
Look up a colour for a value from the palette.
Create a function to lookup a value from the palette.
Get the default colour. Surprise.
Inverts the order of values. Note, the palette is generated from the existing colour map so reapplying a palette will result in reversed colours
Create a new CategoryColourScale from a list of values.
Sets the default colour for the scale when it isn't possible to look one up for a value
Update the colour palette used for the scale
Link to this section Types
@type colour_palette() :: nil | :default | :pastel1 | :warm | list()
Link to this section Functions
Look up a colour for a value from the palette.
Create a function to lookup a value from the palette.
Get the default colour. Surprise.
Inverts the order of values. Note, the palette is generated from the existing colour map so reapplying a palette will result in reversed colours
@spec new(list(), colour_palette()) :: t()
Create a new CategoryColourScale from a list of values.
Optionally attach a colour palette. Pretty well any value list can be used so long as it can be a key in a map.
Sets the default colour for the scale when it isn't possible to look one up for a value
@spec set_palette(t(), colour_palette()) :: t()
Update the colour palette used for the scale