Krn Krn - 6 months ago 24
Python Question

Changing marker style in scatter plot according to third variable

I am dealing with a multi-column dictionary. I want to plot two columns and subsequently change color and style of the markers according to a third and fourth column.

I struggle with changing the marker style in the pylab scatter plot. My approach, which works for color, unfortunately does not work for marker style.

x=[1,2,3,4,5,6]
y=[1,3,4,5,6,7]
m=['k','l','l','k','j','l']

for i in xrange(len(m)):
m[i]=m[i].replace('j','o')
m[i]=m[i].replace('k','x')
m[i]=m[i].replace('l','+')

plt.scatter(x,y,marker=m)
plt.show()

Answer

The problem is that marker can only be a single value and not a list of markers, as the color parmeter.

You can either do a grouping by marker value so you have the x and y lists that have the same marker and plot them:

xs = [[1, 2, 3], [4, 5, 6]]
ys = [[1, 2, 3], [4, 5, 6]]
m = ['o', 'x']
for i in range(len(xs)):
    plt.scatter(xs[i], ys[i], marker=m[i])
plt.show()

Or you can plot every single dot (which I would not recommend):

x=[1,2,3,4,5,6]
y=[1,3,4,5,6,7]
m=['k','l','l','k','j','l']

mapping = {'j' : 'o', 'k': 'x', 'l': '+'}

for i in range(len(x)):
    plt.scatter(x[i], y[i], marker=mapping[m[i]])
plt.show()