Palettes and mappers

Using palettes

Palettes are sequences of RGB(A) hex strings that define a colormap. The sequences you use for defining colormaps can be either lists or tuples. Once you have created a colormap, you can use it with the color attribute of many plot objects from bokeh.plotting.

Bokeh includes several pre-defined palettes, such as the standard Brewer palettes. To use one of those pre-defined palettes, import it from the bokeh.palettes module. When you import “Spectral6”, for example, Bokeh gives you access to a six element list of RGB(A) hex strings from the Brewer “Spectral” colormap:

>>> from bokeh.palettes import Spectral6
>>> Spectral6
['#3288bd', '#99d594', '#e6f598', '#fee08b', '#fc8d59', '#d53e4f']

For a list of all the standard palettes included in Bokeh, see bokeh.palettes.

You can also create custom palettes by defining a sequence of RGB(A) hex strings yourself.

Using mappers

Use Bokeh’s color mappers to encode a sequence of data into a palette of colors that are based on the values in that sequence. You can then set a marker object’s color attribute to your color mapper. Bokeh includes several types of mappers to encode colors:

• factor_cmap(): Maps colors to specific categorical elements. See Bar charts for more detail.

• linear_cmap(): Maps a range of numeric values across the available colors from high to low. For example, a range of [0,99] given the colors [‘red’, ‘green’, ‘blue’] would be mapped as follows:

      x < 0  : 'red'     # values < low are clamped
  0 >= x < 33 : 'red'
  33 >= x < 66 : 'green'
  66 >= x < 99 : 'blue'
  99 >= x      : 'blue'    # values > high are clamped
  

• log_cmap(): Similar to linear_cmap but uses a natural log scale to map the colors.

These mapper functions return a DataSpec property. Pass this property to the color attribute of the glyph you want to use it with.

The dataspec that the mapper function returns includes a bokeh.transform. You can access this data to use the result of the mapper function in a different context. To create a ColorBar, for example:

from bokeh.models import ColorBar, ColumnDataSource
from bokeh.palettes import Spectral6
from bokeh.plotting import figure, show
from bokeh.transform import linear_cmap

x = [1,2,3,4,5,7,8,9,10]
y = [1,2,3,4,5,7,8,9,10]

#Use the field name of the column source
mapper = linear_cmap(field_name='y', palette=Spectral6, low=min(y), high=max(y))

source = ColumnDataSource(dict(x=x,y=y))

p = figure(width=300, height=300, title="Linear Color Map Based on Y")

p.circle(x='x', y='y', line_color=mapper,color=mapper, fill_alpha=1, size=12, source=source)

color_bar = ColorBar(color_mapper=mapper['transform'], width=8)

p.add_layout(color_bar, 'right')

show(p)