CODEWITHSUNDEEP
pythonmatplotlib
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Reputation: 51

Simple dictionary as a matplotlib graph

I am a newbie and trying to use dictionaries and plot graphs with python. I am trying to create a simple line graph with country names on x axis and population on y axis. However I get an error for this code:

#!/usr/bin/python
#
#Dictionary example
#
import sys
import matplotlib.pyplot as plt
import numpy as np

if __name__ == '__main__':

    country_names = [ 'Germany', 'Italy', 'Netherlands', 'France'] #list of countries

    capital_list =['Berlin', 'Rome', 'Amsterdam', 'Paris']#list of capitals to be mapped to countries
    population_list= ['3.5','2.1', '0.3', '2.8'] #list of population of induvidual countries, all figures in Million
    language_list=['German','Italian','Dutch','French'] #list of languages to be mapped to countries


    dictionary_list = [ {'COUNTRY': country, 'CAPITAL': capital, 'POPULATION':population, 'LANGUAGE': lang} for country, capital, population, lang in zip(country_names, capital_list, population_list, language_list)]
    #print(dictionary_list)
    x = [d['CAPITAL'] for d in dictionary_list]
    print x
    y = [d['POPULATION'] for d in dictionary_list ]
    print y

    # create plot space upon which to plot the data
    fig, ax = plt.subplots()

    # add the x-axis and the y-axis to the plot
    ax.plot(x, y);

Here is the error:

['Berlin', 'Rome', 'Amsterdam', 'Paris']
['3.5', '2.1', '0.3', '2.8']
Traceback (most recent call last):
  File "graph.py", line 29, in <module>
    ax.plot(x, y);
  File "/usr/lib/python2.7/dist-packages/matplotlib/__init__.py", line 1814, in inner
    return func(ax, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/matplotlib/axes/_axes.py", line 1425, in plot
    self.add_line(line)
  File "/usr/lib/python2.7/dist-packages/matplotlib/axes/_base.py", line 1708, in add_line
    self._update_line_limits(line)
  File "/usr/lib/python2.7/dist-packages/matplotlib/axes/_base.py", line 1730, in _update_line_limits
    path = line.get_path()
  File "/usr/lib/python2.7/dist-packages/matplotlib/lines.py", line 925, in get_path
    self.recache()
  File "/usr/lib/python2.7/dist-packages/matplotlib/lines.py", line 612, in recache
    x = np.asarray(xconv, np.float_)
  File "/usr/lib/python2.7/dist-packages/numpy/core/numeric.py", line 482, in asarray
    return array(a, dtype, copy=False, order=order)
ValueError: could not convert string to float: Berlin

Why can't x-axis and y-axis have different data types? Why do I have to convert x-axis to float?

Please help.

Thanks

Upvotes: 0

Views: 41

Answers (1)

Sheldore
Sheldore

Reputation: 39042

It seems you are using python 2.7. Your code works fine for me on python 3.6.5. Nevertheless, the problem you are facing can be solved by explicitly converting the population_list to a list of floats before creating the dictionary as

population_list= map(float, ['3.5','2.1', '0.3', '2.8'])

The above generator expression will work for you as you are looping over it. If you want to see the actual list, convert it back to a list as

population_list= list(map(float, ['3.5','2.1', '0.3', '2.8']))

By the way, I do not see a need of dictionary here. You can directly plot the lists after converting the population to float.

enter image description here

Upvotes: 1

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