How to add colorbars to scatterplots created like this?

Question

I create scatterplots with code that, in essence, goes like this

cmap = (matplotlib.color.LinearSegmentedColormap.
        from_list(\'blueWhiteRed\', [\'blu         


        

Answer 1

If you have to use a different marker for each set, you have to do a bit of extra work and force all of the clims to be the same (otherwise they default to scaling from the min/max of the c data per scatter plot).

from pylab import *
import matplotlib.lines as mlines
import itertools
fig = gcf()
ax = fig.gca()

# make some temorary arrays
X = []
Y = []
C = []
cb = None
# generate fake data
markers = ['','o','*','^','v']
cmin = 0
cmax = 1
for record,marker in itertools.izip(range(5),itertools.cycle(mlines.Line2D.filled_markers)):
    x = rand(50)
    y = rand(50)
    c = rand(1)[0] * np.ones(x.shape)
    if cb is None:
        s = ax.scatter(x,y,c=c,marker=markers[record],linewidths=0)
        s.set_clim([cmin,cmax])
        cb = fig.colorbar(s)
    else:
        s = ax.scatter(x,y,c=c,marker=markers[record],linewidths=0)
        s.set_clim([cmin,cmax])

cb.set_label('Cbar Label Here')

thelinewidths=0 sets the width of the border on the shapes, I find that for small shapes the black border can overwhelm the color of the fill.

If you only need one shape you can do this all with a single scatter plot, there is no need to make a separate one for each pass through your loop.

from pylab import *
fig = gcf()
ax = fig.gca()

# make some temorary arrays
X = []
Y = []
C = []
# generate fake data
for record in range(5):
    x = rand(50)
    y = rand(50)
    c = rand(1)[0] * np.ones(x.shape)
    print c
    X.append(x)
    Y.append(y)
    C.append(c)

X = np.hstack(X)
Y = np.hstack(Y)
C = np.hstack(C)

once you have the data all beaten down into a 1D array, make the scatter plot, and keep the returned value:

s = ax.scatter(X,Y,c=C)

You then make your color bar and pass the object returned by scatter as the first argument.

cb = plt.colorbar(s)
cb.set_label('Cbar Label Here')

You need do this so that the color bar knows which color map (both the map and the range) to use.