作为 matplotlib 图的简单字典

Question

我是一个新手，正在尝试使用字典和 python 绘图。 我正在尝试创建一个简单的折线图，x 轴为国家名称，y 轴为人口。但是我收到此代码的错误：

#!/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);

这是错误：

['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

为什么 x 轴和 y 轴不能有不同的数据类型？为什么一定要把x轴转成float？

请帮忙。

谢谢

Answer 1

您似乎正在使用python 2.7。您的代码在python 3.6.5 上对我来说很好。不过，您面临的问题可以通过在创建字典之前将population_list 显式转换为浮点列表来解决

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

上面的生成器表达式将在您循环它时为您工作。如果您想查看实际列表，请将其转换回列表为

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

顺便说一句，我认为这里不需要字典。您可以在将人口转换为浮点数后直接绘制列表。