Scatter plot and Color mapping in Python

Question

I have a range of points x and y stored in numpy arrays  Those represent x t  and y t  where t 0   T-1  I am plotting a scatter plot using  import matplotlib pyplot as plt  plt scatter x y  plt show     I would like to have a colormap representing the time  therefore coloring the points depending on the index in the numpy arrays    What is the easiest way to do so

User · Answer

Subplot Colorbar  For subplots with scatter  you can trick a colorbar onto your axes by building the  mappable  with the help of a secondary figure and then adding it to your original plot   As a continuation of the above example   import numpy as np import matplotlib pyplot as plt  x   np arange 10  y   x t   x fig   ax1  ax2    plt subplots 1  2  ax1 scatter x  y  c t  cmap  viridis   ax2 scatter x  y  c t  cmap  viridis r       Build your secondary mirror axes  fig2   ax3  ax4    plt subplots 1  2     Build maps that parallel the color-coded data   NOTE 1  imshow requires a 2-D array as input   NOTE 2  You must use the same cmap tag as above for it match map1   ax3 imshow np stack  t  t   cmap  viridis   map2   ax4 imshow np stack  t  t   cmap  viridis r      Add your maps onto your original figure axes fig colorbar map1  ax ax1  fig colorbar map2  ax ax2  plt show       Note that you will also output a secondary figure that you can ignore

User · Answer

Here is an example  import numpy as np import matplotlib pyplot as plt  x   np random rand 100  y   np random rand 100  t   np arange 100   plt scatter x  y  c t  plt show     Here you are setting the color based on the index  t  which is just an array of  1  2       100     Perhaps an easier-to-understand example is the slightly simpler  import numpy as np import matplotlib pyplot as plt  x   np arange 100  y   x t   x plt scatter x  y  c t  plt show       Note that the array you pass as c doesn t need to have any particular order or type  i e  it doesn t need to be sorted or integers as in these examples   The plotting routine will scale the colormap such that the minimum maximum values in c correspond to the bottom top of the colormap   Colormaps  You can change the colormap by adding  import matplotlib cm as cm plt scatter x  y  c t  cmap cm cmap name    Importing matplotlib cm is optional as you can call colormaps as cmap  cmap name  just as well   There is a reference page of colormaps showing what each looks like   Also know that you can reverse a colormap by simply calling it as cmap name r   So either  plt scatter x  y  c t  cmap cm cmap name r    or plt scatter x  y  c t  cmap  cmap name r     will work   Examples are  jet r  or cm plasma r   Here s an example with the new 1 5 colormap viridis   import numpy as np import matplotlib pyplot as plt  x   np arange 100  y   x t   x fig   ax1  ax2    plt subplots 1  2  ax1 scatter x  y  c t  cmap  viridis   ax2 scatter x  y  c t  cmap  viridis r   plt show       Colorbars  You can add a colorbar by using  plt scatter x  y  c t  cmap  viridis   plt colorbar   plt show       Note that if you are using figures and subplots explicitly  e g  fig  ax   plt subplots   or ax   fig add subplot 111    adding a colorbar can be a bit more involved  Good examples can be found here for a single subplot colorbar and here for 2 subplots 1 colorbar

User · Answer

To add to wflynny s answer above  you can find the available colormaps here  Example    import matplotlib cm as cm plt scatter x  y  c t  cmap cm jet    or alternatively    plt scatter x  y  c t  cmap  jet

[python] Scatter plot and Color mapping in Python

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