Stackplot using list of dictionary values (Python 3.x)

Question

I am trying to make a stackplot from a dictionary where the value is a list of floats between 0 and 1 and the index of the value in the list is the time (t1, t2, ...tn) of measurement. All keys have the same number of values. For example:

a = {1:[0.3,0.5,0.7], 2:[0.4,0.6,0.8], 5:[0.1,0.15,0.20]}

so that at t2: a[1] = 0.5, a[2] = 0.6, and a[5] = 0.15, and so on at the other indices of the list of values.

I'm going for a stackplot like the one here with the indices of the value list on the x-axis and the value of a[i] at that index on the y-axis , but can't figure out how to adapt that code or the matplotlib example to a dictionary.

Python version: 3.4

Error (for both my data and toy data set): TypeError: ufunc 'isfinite' not supported for the input types, and the inputs could not be safely coerced to any supported types according to the casting rule ''safe''

Suggestions?

that is an incorrect dictionary syntax. a dictionary is written like a = {1:[0.3,0.5,0.7], 2:[0.4,0.6,0.8]} — awbemauler
– awbemauler, Commented Jul 31, 2015 at 19:22
Noted, that was a typo in the example. Not a problem I encountered in my true dictionary. — bradi
– bradi, Commented Jul 31, 2015 at 19:24
Am I right in assuming that you don't actually need the keys of a? — j-i-l
– j-i-l, Commented Jul 31, 2015 at 19:48
@jojo Right -- the keys of a are just identifiers, so the only time I'd use them is in building the legend. — bradi
– bradi, Commented Jul 31, 2015 at 19:50

j-i-l · Accepted Answer · 2015-07-31 21:31:40Z

3

UPDATE - The error you are getting is because matplotlib is somehow not happy with the view you are getting from dict.values(). Note that this is only a problem of python 3.x as for python 2.x dict.values() returns a list. You can simply avoid this problem by converting the view into a normal list, so list(dict.values()).

Here is the matplotlib example using a dict, working for both python 2.x and 3.x:

import numpy as np
from matplotlib import pyplot as plt

fnx = lambda : np.random.randint(5, 50, 10).astype(np.float64)
d = {i: v for i, v in enumerate(np.row_stack((fnx(), fnx(), fnx())))}
# d looks basically like your a
x = range(len(d[0]))
y = list(d.values()) # d.values() returns a view in python 3.x
fig, ax = plt.subplots()
ax.stackplot(x, y)
plt.show()

edited Jul 31, 2015 at 21:31

answered Jul 31, 2015 at 19:37

j-i-l

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5 Comments

bradi Over a year ago

range() replaced xrange() in Python 3+

bradi Over a year ago

Even once I remove .values, I still get the TypeError. Would it matter that some of the decimal numbers I use are particularly long?

j-i-l Over a year ago

@bradi note that Decimal type is not supported so you should be fine if you convert your dictionary a to contain only floats.

j-i-l Over a year ago

@bradi to convert all the entries in a to floats: a = {i: map(lambda x: float(x), a[i]) for i in a}

j-i-l Over a year ago

@bradi The issue is that dict.values() is a view in python 3.x. This is what was causing the error. y = list(d.values()) will get you there (finally :P).

Diziet Asahi · Accepted Answer · 2015-07-31 19:38:42Z

0

It's not entirely clear what you want to achieve, but if I understood you, this should work:

import matplotlib.pyplot as plt
a = {1:[0.3,0.5,0.7], 2:[0.4,0.6,0.8], 5:[0.1,0.15,0.20]}
plt.stackplot(a.keys(),a.values())

answered Jul 31, 2015 at 19:38

Diziet Asahi

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