Matplotlib color according to class labels

Question

I have two vectors  one with values and one with class labels like 1 2 3 etc    I would like to plot all the points that belong to class 1 in red  to class 2 in blue  to class 3 in green etc  How can I do that

User · Answer

Assuming that you have your data in a 2d array, this should work:

import numpy
import pylab
xy = numpy.zeros((2, 1000))
xy[0] = range(1000)
xy[1] = range(1000)
colors = [int(i % 23) for i in xy[0]]
pylab.scatter(xy[0], xy[1], c=colors)
pylab.show()

You can also set a cmap attribute to control which colors will appear through use of a colormap; i.e. replace the pylab.scatter line with:

pylab.scatter(xy[0], xy[1], c=colors, cmap=pylab.cm.cool)

A list of color maps can be found here

User · Answer

The accepted answer has it spot on  but if you might want to specify which class label should be assigned to a specific color or label you could do the following  I did a little label gymnastics with the colorbar  but making the plot itself reduces to a nice one-liner  This works great for plotting the results from classifications done with sklearn  Each label matches a  x y  coordinate    import matplotlib import matplotlib pyplot as plt import numpy as np  x    4 8 12 16 1 4 9 16  y    1 4 9 16 4 8 12 3  label    0 1 2 3 0 1 2 3  colors     red   green   blue   purple    fig   plt figure figsize  8 8   plt scatter x  y  c label  cmap matplotlib colors ListedColormap colors    cb   plt colorbar   loc   np arange 0 max label  max label  float len colors    cb set ticks loc  cb set ticklabels colors      Using a slightly modified version of this answer  one can generalise the above for N colors as follows   import numpy as np import matplotlib as mpl import matplotlib pyplot as plt  N   23   Number of labels    setup the plot fig  ax   plt subplots 1 1  figsize  6 6     define the data x   np random rand 1000  y   np random rand 1000  tag   np random randint 0 N 1000    Tag each point with a corresponding label        define the colormap cmap   plt cm jet   extract all colors from the  jet map cmaplist    cmap i  for i in range cmap N     create the new map cmap   cmap from list  Custom cmap   cmaplist  cmap N     define the bins and normalize bounds   np linspace 0 N N 1  norm   mpl colors BoundaryNorm bounds  cmap N     make the scatter scat   ax scatter x y c tag s np random randint 100 500 N  cmap cmap      norm norm    create the colorbar cb   plt colorbar scat  spacing  proportional  ticks bounds  cb set label  Custom cbar   ax set title  Discrete color mappings   plt show     Which gives

User · Answer

A simple solution is to assign color for each class  This way  we can control how each color is for each class  For example   arr1    1  2  3  4  5  arr2    2  3  3  4  4  labl    0  1  1  0  0  color    red  if l    0 else  green  for l in labl  plt scatter arr1  arr2  color color

[python] Matplotlib color according to class labels

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