Matplotlib scatterplot colour as a function of a third variable

Question

I want to make a scatterplot  using matplotlib  where the points are shaded according to a third variable  I ve got very close with this   plt scatter w  M  c p  marker  s     where w and M are the datapoints and p is the variable I want to shade with respect to  However I want to do it in greyscale rather than colour  Can anyone help

User · Answer

There s no need to manually set the colors  Instead  specify a grayscale colormap     import numpy as np import matplotlib pyplot as plt    Generate data    x   np random random 10  y   np random random 10     Plot    plt scatter x  y  c y  s 500  plt gray    plt show       Or  if you d prefer a wider range of colormaps  you can also specify the cmap kwarg to scatter   To use the reversed version of any of these  just specify the   r  version of any of them  E g  gray r instead of gray   There are several different grayscale colormaps pre-made  e g  gray  gist yarg  binary  etc      import matplotlib pyplot as plt import numpy as np    Generate data    x   np random random 10  y   np random random 10   plt scatter x  y  c y  s 500  cmap  gray   plt show

User · Answer

In matplotlib grey colors can be given as a string of a numerical value between 0-1  For example c    0 1    Then you can convert your third variable in a value inside this range and to use it to color your points  In the following example I used the y position of the point as the value that determines the color     from matplotlib import pyplot as plt  x    1  2  3  4  5  6  7  8  9  y    125  32  54  253  67  87  233  56  67   color    str item 255   for item in y   plt scatter x  y  s 500  c color   plt show

User · Answer

Sometimes you may need to plot color precisely based on the x-value case  For example  you may have a dataframe with 3 types of variables and some data points  And you want to do following    Plot points corresponding to Physical variable  A  in RED  Plot points corresponding to Physical variable  B  in BLUE  Plot points corresponding to Physical variable  C  in GREEN    In this case  you may have to write to short function to map the x-values to corresponding color names as a list and then pass on that list to the plt scatter command   x   A   B   B   C   A   B   y  15 30 25 18 22 13     Function to map the colors as a list from the input list of x variables def pltcolor lst       cols        for l in lst          if l   A               cols append  red           elif l   B               cols append  blue           else              cols append  green       return cols   Create the colors list using the function above cols pltcolor x   plt scatter x x y y s 500 c cols   Pass on the list created by the function here plt grid True  plt show

[python] Matplotlib scatterplot; colour as a function of a third variable

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