pandas 如何在matplotlib中按不同组绘制直方图？
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How to plot a histogram by different groups in matplotlib?
提问by Zelong
I have a table like:
我有一张像：
value type
10 0
12 1
13 1
14 2
Generate a dummy data:
生成虚拟数据：
import numpy as np
value = np.random.randint(1, 20, 10)
type = np.random.choice([0, 1, 2], 10)
I want to accomplish a task in Python 3 with matplotlib (v1.4):
我想用 matplotlib (v1.4) 在 Python 3 中完成一项任务：
- plot a histogram of
value - group by
type, i.e. use different colors to differentiate types - the position of the "bars" should be "dodge", i.e. side by side
- since the range of value is small, I would use
identityfor bins, i.e. the width of a bin is 1
- 绘制直方图
value - group by
type，即使用不同的颜色来区分类型 - “酒吧”的位置应该是“躲避”，即并排
- 由于值的范围很小，我将
identity用于垃圾箱，即垃圾箱的宽度为 1
The questionsare:
该问题是：
- how to assign colors to bars based on the values of
typeand draw colors from colormap (e.g.Accentor other cmap in matplotlib)? I don't want to use named color(i.e.'b', 'k', 'r') - the bars in my histogram overlap each other, how to "dodge" the bars?
- 如何根据
type颜色图（例如Accent或 matplotlib 中的其他 cmap）的值和绘制颜色为条形分配颜色？我不想使用命名颜色（即'b', 'k', 'r'） - 我的直方图中的条形相互重叠，如何“躲避”条形？
Note(lest the post will be down voted and deemed to be "naive")
注意（以免帖子被否决并被视为“幼稚”）
- I have tried on Seaborn, matplotlib and
pandas.plotfor two hours and failed to get the desired histogram. - I read the examples and Users' Guide of matplotlib. Surprisingly, I found no tutorial about how to assign colors from colormap.
- I have searched on Google but failed to find a succinct example.
- I guess one could accomplish the task with
matplotlib.pyplot, without import a bunch of modules such asmatplotlib.cm,matplotlib.colors.
- 我已经尝试了 Seaborn、matplotlib 和
pandas.plot两个小时，但未能获得所需的直方图。 - 我阅读了 matplotlib 的示例和用户指南。令人惊讶的是，我没有找到关于如何从颜色图中分配颜色的教程。
- 我在谷歌上搜索过，但没有找到一个简洁的例子。
- 我想可以使用 完成任务
matplotlib.pyplot，而无需导入一堆模块，例如matplotlib.cm,matplotlib.colors。
回答by maxymoo
For your first question, we can create a dummy column equal to 1, and then generate counts by summing this column, grouped by value and type.
对于您的第一个问题，我们可以创建一个等于 1 的虚拟列，然后通过对按值和类型分组的此列求和来生成计数。
For your second question you can pass the colormap directly into plotusing the colormapparameter:
对于您的第二个问题，您可以plot使用colormap参数将颜色图直接传递给：
import pandas as pd
import matplotlib.pyplot as plt
import matplotlib.cm as cm
import seaborn
seaborn.set() #make the plots look pretty
df = pd.DataFrame({'value': value, 'type': type})
df['dummy'] = 1
ag = df.groupby(['value','type']).sum().unstack()
ag.columns = ag.columns.droplevel()
ag.plot(kind = 'bar', colormap = cm.Accent, width = 1)
plt.show()
