How to generate random colors in matplotlib

Question

What s the trivial example of how to generate random colors for passing to plotting functions   I m calling scatter inside a loop and want each plot a different color   for X Y in data     scatter X  Y  c          c    a color  c can be a single color format string  or a sequence of color specifications of length N  or a sequence of N numbers to be mapped to colors using the cmap and norm specified via kwargs  see below   Note that c should not be a single numeric RGB or RGBA sequence because that is indistinguishable from an array of values to be colormapped  c can be a 2-D array in which the rows are RGB or RGBA  however

User · Answer

If you want to ensure the colours are distinct - but don't know how many colours are needed. Try something like this. It selects colours from opposite sides of the spectrum and systematically increases granularity.

import math

def calc(val, max = 16):
    if val < 1:
        return 0
    if val == 1:
        return max

    l = math.floor(math.log2(val-1))    #level 
    d = max/2**(l+1)                    #devision
    n = val-2**l                        #node
    return d*(2*n-1)

import matplotlib.pyplot as plt

N = 16
cmap = cmap = plt.cm.get_cmap('gist_rainbow', N)

fig, axs = plt.subplots(2)
for ax in axs:
    ax.set_xlim([ 0, N])
    ax.set_ylim([-0.5, 0.5])
    ax.set_yticks([])

for i in range(0,N+1):
    v = int(calc(i, max = N))
    rect0 = plt.Rectangle((i, -0.5), 1, 1, facecolor=cmap(i))
    rect1 = plt.Rectangle((i, -0.5), 1, 1, facecolor=cmap(v))
    axs[0].add_artist(rect0)
    axs[1].add_artist(rect1)

plt.xticks(range(0, N), [int(calc(i, N)) for i in range(0, N)])
plt.show()

output

Thanks to @Ali for providing the base implementation.

User · Answer

Since the question is How to generate random colors in matplotlib  and as I was searching for an answer concerning pie plots  I think it is worth to put an answer here  for pies   import numpy as np from random import sample import matplotlib pyplot as plt import matplotlib colors as pltc all colors    k for k v in pltc cnames items     fracs   np array  600  179  154  139  126  1185   labels     label1    label2    label3    label4    label5    label6   explode     fracs    max fracs   astype int    20  tolist    for val in range 2       colors   sample all colors  len fracs       plt figure figsize  8 8       plt pie fracs  labels labels  autopct   1 1f                  shadow True  explode explode  colors colors      plt legend labels  loc  1 05  0 7   shadow True      plt show     Output

User · Answer

When less than 9 datasets   colors    bgrcmykw  color index   0  for X Y in data      scatter X Y  c colors color index       color index    1

User · Answer

For some time I was really annoyed by the fact that matplotlib doesn t generate colormaps with random colors  as this is a common need for segmentation and clustering tasks    By just generating random colors we may end with some that are too bright or too dark  making visualization difficult  Also  usually we need the first or last color to be black  representing the background or outliers  So I ve wrote a small function for my everyday work  Here s the behavior of it   new cmap   rand cmap 100  type  bright   first color black True  last color black False  verbose True      Than you just use new cmap as your colormap on matplotlib   ax scatter X Y  c label  cmap new cmap  vmin 0  vmax num labels    The code is here   def rand cmap nlabels  type  bright   first color black True  last color black False  verbose True               Creates a random colormap to be used together with matplotlib  Useful for segmentation tasks      param nlabels  Number of labels  size of colormap       param type   bright  for strong colors   soft  for pastel colors      param first color black  Option to use first color as black  True or False      param last color black  Option to use last color as black  True or False      param verbose  Prints the number of labels and shows the colormap  True or False      return  colormap for matplotlib             from matplotlib colors import LinearSegmentedColormap     import colorsys     import numpy as np       if type not in   bright    soft            print   Please choose  bright  or  soft  for type           return      if verbose          print  Number of labels      str nlabels          Generate color map for bright colors  based on hsv     if type     bright           randHSVcolors     np random uniform low 0 0  high 1                             np random uniform low 0 2  high 1                             np random uniform low 0 9  high 1   for i in xrange nlabels              Convert HSV list to RGB         randRGBcolors              for HSVcolor in randHSVcolors              randRGBcolors append colorsys hsv to rgb HSVcolor 0   HSVcolor 1   HSVcolor 2             if first color black              randRGBcolors 0     0  0  0           if last color black              randRGBcolors -1     0  0  0           random colormap   LinearSegmentedColormap from list  new map   randRGBcolors  N nlabels         Generate soft pastel colors  by limiting the RGB spectrum     if type     soft           low   0 6         high   0 95         randRGBcolors     np random uniform low low  high high                             np random uniform low low  high high                             np random uniform low low  high high   for i in xrange nlabels            if first color black              randRGBcolors 0     0  0  0           if last color black              randRGBcolors -1     0  0  0          random colormap   LinearSegmentedColormap from list  new map   randRGBcolors  N nlabels         Display colorbar     if verbose          from matplotlib import colors  colorbar         from matplotlib import pyplot as plt         fig  ax   plt subplots 1  1  figsize  15  0 5            bounds   np linspace 0  nlabels  nlabels   1          norm   colors BoundaryNorm bounds  nlabels           cb   colorbar ColorbarBase ax  cmap random colormap  norm norm  spacing  proportional   ticks None                                     boundaries bounds  format   1i   orientation u horizontal        return random colormap   It s also on github  https   github com delestro rand cmap

User · Answer

Based on Ali s and Champitoad s answer   If you want to try different palettes for the same  you can do this in a few lines   cmap plt cm get cmap plt cm viridis 143    143 being the number of colours you re sampling  I picked 143 because the entire range of colours on the colormap comes into play here  What you can do is sample the nth colour every iteration to get the colormap effect   n 20 for i  x y  in enumerate points       plt scatter x y c cmap n i

User · Answer

enter code here  import numpy as np  clrs   np linspace  0  1  18      It will generate    color only for 18 for more change the number np random shuffle clrs  colors      for i in range 0  72  4       idx   np arange  0  18  1       np random shuffle idx      r   clrs idx 0       g   clrs idx 1       b   clrs idx 2       a   clrs idx 3       colors append  r  g  b  a

User · Answer

Here is a more concise version of Ali s answer giving one distinct color per plot    import matplotlib pyplot as plt  N   len data  cmap   plt cm get cmap  hsv   N 1  for i in range N       X Y   data i      plt scatter X  Y  c cmap i

User · Answer

I m calling scatter inside a loop and want each plot in a different color    Based on that  and on your answer  It seems to me that you actually want n distinct colors for your datasets  you want to map the integer indices 0  1       n-1 to distinct RGB colors  Something like     Here is the function to do it   import matplotlib pyplot as plt  def get cmap n  name  hsv           Returns a function that maps each index in 0  1       n-1 to a distinct      RGB color  the keyword argument name must be a standard mpl colormap name         return plt cm get cmap name  n    Usage in your pseudo-code snippet in the question   cmap   get cmap len data   for i   X  Y  in enumerate data      scatter X  Y  c cmap i       I generated the figure in my answer with the following code   import matplotlib pyplot as plt  def get cmap n  name  hsv           Returns a function that maps each index in 0  1       n-1 to a distinct      RGB color  the keyword argument name must be a standard mpl colormap name         return plt cm get cmap name  n   def main        N   30     fig plt figure       ax fig add subplot 111         plt axis  scaled       ax set xlim   0  N       ax set ylim  -0 5  0 5       cmap   get cmap N      for i in range N           rect   plt Rectangle  i  -0 5   1  1  facecolor cmap i           ax add artist rect      ax set yticks         plt show    if   name       main         main     Tested with both Python 2 7  amp  matplotlib 1 5  and with Python 3 5  amp  matplotlib 2 0  It works as expected

User · Answer

elaborating  john-mee  s answer  if you have arbitrarily long data but don t need strictly unique colors   for python 2   from itertools import cycle cycol   cycle  bgrcmk    for X Y in data      scatter X  Y  c cycol next      for python 3   from itertools import cycle cycol   cycle  bgrcmk    for X Y in data      scatter X  Y  c next cycol     this has the advantage that the colors are easy to control and that it s short

User · Answer

for X Y in data     scatter X  Y  c numpy random rand 3

User · Answer

Improving the answer https   stackoverflow com a 14720445 6654512 to work with Python3  That piece of code would sometimes generate numbers greater than 1 and matplotlib would throw an error   for X Y in data     scatter X  Y  c numpy random random 3

[python] How to generate random colors in matplotlib?

Examples related to python

Examples related to matplotlib