Plot a histogram from a Dictionary

Question

I created a dictionary that counts the occurrences in a list of every key and I would now like to plot the histogram of its content.

This is the content of the dictionary I want to plot:

{1: 27, 34: 1, 3: 72, 4: 62, 5: 33, 6: 36, 7: 20, 8: 12, 9: 9, 10: 6, 11: 5, 12: 8, 2: 74, 14: 4, 15: 3, 16: 1, 17: 1, 18: 1, 19: 1, 21: 1, 27: 2}

So far I wrote this:

import numpy as np
import matplotlib.pyplot as plt

pos = np.arange(len(myDictionary.keys()))
width = 1.0     # gives histogram aspect to the bar diagram

ax = plt.axes()
ax.set_xticks(pos + (width / 2))
ax.set_xticklabels(myDictionary.keys())

plt.bar(myDictionary.keys(), ******, width, color='g')
#                            ^^^^^^ what should I put here?
plt.show()

I tried by simply doing

plt.bar(myDictionary.keys(), myDictionary, width, color='g')

but this is the result:

enter image description here

and I don’t know why the 3 bars are shifted and also I’d like the histogram to be displayed in a ordered fashion.

Can somebody tell me how to do it?

Asked By: Matteo

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Source

Answer 1

values = [] #in same order as traversing keys
keys = [] #also needed to preserve order
for key in myDictionary.keys():
  keys.append(key)
  values.append(myDictionary[key])

Use ‘keys’ and ‘values’. This ensures that the order is preserved.

Answered By: mcsilvio

Answer 2

You can use the function for plotting histograms like this:

a = np.random.random_integers(0,10,20) #example list of values
plt.hist(a)
plt.show()

Or you can use myDictionary just like this:

plt.bar(myDictionary.keys(), myDictionary.values(), width, color='g')

Answered By: Alvaro Fuentes

Answer 3

With Python 3 you need to use list(your_dict.keys()) instead of your_dict.keys() (otherwise you get TypeError: ‘dict_keys’ object does not support indexing):

import matplotlib.pyplot as plt

dictionary = {1: 27, 34: 1, 3: 72, 4: 62, 5: 33, 6: 36, 7: 20, 8: 12, 9: 9, 10: 6, 11: 5, 
              12: 8, 2: 74, 14: 4, 15: 3, 16: 1, 17: 1, 18: 1, 19: 1, 21: 1, 27: 2}
plt.bar(list(dictionary.keys()), dictionary.values(), color='g')
plt.show()

Tested with Matplotlib 2.0.0 and python 3.5.

FYI: Plotting a python dict in order of key values

Answered By: Franck Dernoncourt

Answer 4

In case the keys of the myDictionary are not uniformed distributed, its helpful to use the keys as str:

plt.bar([ str(i) for i in myDictionary.keys()], myDictionary.values(), color='g')

Answered By: organicData

Answer 5

If you really want to use the plt.hist function (for example to use the bins keyword), you can always convert your Counter to a list

With your code :

mydict = {1: 27, 34: 1, 3: 72, 4: 62, 5: 33, 6: 36, 7: 20, 8: 12, 9: 9, 10: 6, 11: 5, 12: 8, 2: 74, 14: 4, 15: 3, 16: 1, 17: 1, 18: 1, 19: 1, 21: 1, 27: 2}

mylist = [key for key, val in mydict.items() for _ in range(val)]
plt.hist(mylist, bins=20)

will output

plt.hist(mylist, bins=5)

will output

Answered By: Gabriel

Plot a histogram from a Dictionary

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