python - 如何使用 pandas 将两个 CSV 文档合并在一起并绘制条形图？

Question

数据1：shanghaiData.csv

数据2：timesData.csv

我只是在学习使用来自 CSV 和可视化的数据。我正在尝试合并两个 CSV 表，然后在特定大学的条形图上绘制两个世界排名。

我的代码是：

import pandas as pd
import matplotlib
times_df = pd.read_csv("timesData.csv")
shanghai_df = pd.read_csv("shanghaiData.csv")
combined = times_df.merge(shanghai_df, on='university_name', how='left')
combined = combined.loc[combined['university_name']=='Harvard University']
combined.plot(
    kind = 'bar',
    x = 'year_y',
    y = ['world_rank_x', 'world_rank_y']
)

TypeError                                 Traceback (most recent call last)
<ipython-input-1-e360afadaed4> in <module>
      3 combined.loc[combined['university_name']=='Harvard University']
      4 combined = combined.loc[combined['university_name']=='Harvard University']
----> 5 combined.plot(
      6     kind = 'bar',
      7     x = 'year_y',

/usr/lib/python3.9/site-packages/pandas/plotting/_core.py in __call__(self, *args, **kwargs)
    970                     data.columns = label_name
    971 
--> 972         return plot_backend.plot(data, kind=kind, **kwargs)
    973 
    974     __call__.__doc__ = __doc__

/usr/lib/python3.9/site-packages/pandas/plotting/_matplotlib/__init__.py in plot(data, kind, **kwargs)
     69             kwargs["ax"] = getattr(ax, "left_ax", ax)
     70     plot_obj = PLOT_CLASSES[kind](data, **kwargs)
---> 71     plot_obj.generate()
     72     plot_obj.draw()
     73     return plot_obj.result

/usr/lib/python3.9/site-packages/pandas/plotting/_matplotlib/core.py in generate(self)
    284     def generate(self):
    285         self._args_adjust()
--> 286         self._compute_plot_data()
    287         self._setup_subplots()
    288         self._make_plot()

/usr/lib/python3.9/site-packages/pandas/plotting/_matplotlib/core.py in _compute_plot_data(self)
    451         # no non-numeric frames or series allowed
    452         if is_empty:
--> 453             raise TypeError("no numeric data to plot")
    454 
    455         self.data = numeric_data.apply(self._convert_to_ndarray)

TypeError: no numeric data to plot

如果我尝试将年份转换为整数，我仍然会收到错误消息。

combined['year_y'] = combined['year_y'].astype(int)

标签： pythonpandascsvmatplotlibmerge

Answer 1

我不确定您的输出以及为什么要绘制条形图，但我更改了您的代码并进行了更正。更改这行代码：

import matplotlib.pyplot as plt

plt.bar(combined['year_y'], combined['world_rank_x'])

最后：

import pandas as pd
import matplotlib.pyplot as plt

times_df = pd.read_csv("timesData.csv")
shanghai_df = pd.read_csv("shanghaiData.csv")

combined = times_df.merge(shanghai_df, on='university_name', how='left')
combined = combined.loc[combined['university_name']=='Harvard University']

plt.bar(combined['year_y'], combined['world_rank_x'])

如果你想在一个图中有两个条形图，你可以使用这个代码：

import numpy as np
import matplotlib.pyplot as plt
 

barWidth = 0.25
fig = plt.subplots(figsize =(12, 8))
 

world_rank_x = [2, 2, 2, 2, 2]
world_rank_y = [6, 6, 6, 6, 6]

 
br1 = np.arange(len(world_rank_x))
br2 = [x + barWidth for x in br1]
 
plt.bar(br1, world_rank_x, color ='r', width = barWidth,
        edgecolor ='grey', label ='world_rank_x')
plt.bar(br2, world_rank_y, color ='g', width = barWidth,
        edgecolor ='grey', label ='world_rank_y')

 
plt.xlabel('Year', fontweight ='bold', fontsize = 15)
plt.ylabel('world rank', fontweight ='bold', fontsize = 15)
plt.xticks([r+(barWidth)/2 for r in range(len(world_rank_x))],
        ['2015', '2016', '2017', '2018', '2019'])
 
plt.legend()
plt.show()

输出：