Plot edges of a tree in Python

Question

What is an effective way to plot a list of coordinates in the form [(x1,y1),(x2,y2)], where each pair of coordinates is connected by a line (as shown below). I'd like to avoid use of non-core packages (core being pandas, matplotlib, numpy, ...)

Example:

c = [[(0, 4), (1, 3)],
     [(0, 4), (1, 5)],
     [(1, 3), (2, 2)],
     [(1, 3), (2, 4)],
     [(1, 5), (2, 4)],
     [(1, 5), (2, 6)],
     [(2, 2), (3, 1)],
     [(2, 2), (3, 3)],
     [(2, 4), (3, 3)],
     [(2, 4), (3, 5)],
     [(2, 6), (3, 5)],
     [(2, 6), (3, 7)]]

to be plotted as (with labels):

You said: "where each pair of coordinates is connected by a line". What is the rule of connecting coordinates? For example, you did not connect (0, 4) and (2, 4). — dopstar
– dopstar, Commented Nov 15, 2015 at 13:47
I think this might be helpful https://github.com/erocarrera/pydot — Nader Hisham
– Nader Hisham, Commented Nov 15, 2015 at 14:47
@dopstar: good question. There is no pair [(0,4),(2,4)], so we do not connect it with a line :) However, there is a pair [(0, 4), (1, 3)], so we do connect it (as shown). Should be fairly straight forward, but let me know if further clarity is needed. — Oleg Melnikov
– Oleg Melnikov, Commented Nov 15, 2015 at 15:00
I believe you're looking for something like this: matplotlib.org/users/path_tutorial.html — Adam Acosta
– Adam Acosta, Commented Nov 15, 2015 at 15:13
@EmilyHill Ok I get you. By the way your data is wrong (1, 5) does not connect to (2, 4) in the data but it is in the plot. — dopstar
– dopstar, Commented Nov 15, 2015 at 15:23

dopstar · Accepted Answer · 2015-11-15 15:26:41Z

2

In terms of the 'effective way' I'm not sure. What follows is the working way which I think can be tuned/tweaked to be 'more effective'?

import matplotlib.pyplot as plt

c = [[(0, 4), (1, 3)],
     [(0, 4), (1, 5)],
     [(1, 3), (2, 2)],
     [(1, 3), (2, 4)],
     [(1, 5), (2, 4)],  # I changed this to match your plot
     [(1, 5), (2, 6)],
     [(2, 2), (3, 1)],
     [(2, 2), (3, 3)],
     [(2, 4), (3, 3)],
     [(2, 4), (3, 5)],
     [(2, 6), (3, 5)],
     [(2, 6), (3, 7)]]

fig = plt.figure()
ax = fig.add_subplot(111)

annotated = set()
for l in c:
    d = [[p[0] for p in l], [p[1] for p in l]]
    ax.plot(d[0], d[1], 'k-*')
    for p in l:
        annotated.add(p)

for p in annotated:
    ax.annotate(str(p), xy=p)

plt.xlim([0, 3.5])
plt.ylim([0, 8])
plt.show()

answered Nov 15, 2015 at 15:26

dopstar

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1 Comment

Oleg Melnikov Over a year ago

Nicely engineered! Thanks!

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