Plotting a dictionary with multiple values per key

Question

I have a dictionary that looks like this:

1: ['4026', '4024', '1940', '2912', '2916], 2: ['3139', '2464'], 3:['212']...

For a few hundred keys, I'd like to plot them with the key as y for its set of x values, I tried this bit of code which gives the error underneath:

for rank, structs in b.iteritems():
    y = b.keys()
    x = b.values()
    ax.plot(x, y, 'ro')
    plt.show()

ValueError: setting an array element with a sequence

I'm at a bit of a loss on how to proceed so any help would be greatly appreciated!

Answer 1

You need to construct your list of Xs and Ys manually:

In [258]: b={1: ['4026', '4024', '1940', '2912', '2916'], 2: ['3139', '2464'], 3:['212']}

In [259]: xs, ys=zip(*((int(x), k) for k in b for x in b[k]))

In [260]: xs, ys
Out[260]: ((4026, 4024, 1940, 2912, 2916, 3139, 2464, 212), (1, 1, 1, 1, 1, 2, 2, 3))

In [261]: plt.plot(xs, ys, 'ro')
     ...: plt.show()

resulting:

Answer 2

1) Repeat your x values

plot expects a list of x values and a list of y values which have to have the same length. That's why you have to repeat the rank value several times. itertools.repeat() can do that for you.

2) change your iterator

iteritems() already returns a tuple (key,value). You don't have to use keys() and items().

Here's the code:

import itertools
for rank, structs in b.iteritems():
    x = list(itertools.repeat(rank, len(structs)))
    plt.plot(x,structs,'ro')

3) combine the plots

Using your code, you'd produce one plot per item in the dictionary. I guess you rather want to plot them within a single graph. If so, change your code accrodingly:

import itertools
x = []
y = []
for rank, structs in b.iteritems():
    x.extend(list(itertools.repeat(rank, len(structs))))
    y.extend(structs)
plt.plot(x,y,'ro')

4) example

Here's an example using your data:

import itertools
import matplotlib.pyplot as plt
d = {1: ['4026', '4024', '1940', '2912', '2916'], 2: ['3139', '2464'], 3:['212']}
x= []
y= []
for k, v in d.iteritems():
    x.extend(list(itertools.repeat(k, len(v))))
    y.extend(v)
plt.xlim(0,5)
plt.plot(x,y,'ro')