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

The answer to this can be to only plot a single scatter, which would then directly allow for a colobar to be created. This involves putting the markers into the PathCollection created by the scatter a posteriori, but it can be easily placed in a function. This function comes from my answer on another question, but is directly applicable here.

Taking the data from @PaulH's post this would look like

import numpy as np    
import pandas as pd
import matplotlib.pyplot as plt

def mscatter(x,y,ax=None, m=None, **kw):
    import matplotlib.markers as mmarkers
    ax = ax or plt.gca()
    sc = ax.scatter(x,y,**kw)
    if (m is not None) and (len(m)==len(x)):
        paths = []
        for marker in m:
            if isinstance(marker, mmarkers.MarkerStyle):
                marker_obj = marker
            else:
                marker_obj = mmarkers.MarkerStyle(marker)
            path = marker_obj.get_path().transformed(
                        marker_obj.get_transform())
            paths.append(path)
        sc.set_paths(paths)
    return sc


markers = ['s', 'o', '^']
records = []
for n in range(37):
    records.append([np.random.normal(), np.random.normal(), np.random.normal(), 
                    markers[np.random.randint(0, high=3)]])

records = pd.DataFrame(records, columns=['x', 'y', 'z', 'marker'])

fig, ax = plt.subplots()
sc = mscatter(records.x, records.y, c=records.z, m=records.marker, ax=ax)
fig.colorbar(sc, ax=ax)

plt.show()