Python 如何使用 matplotlib 在 x 轴上针对特定日期绘制数据

How to plot data against specific dates on the x-axis using matplotlib

提问by Kit

I have a dataset consisting of date-value pairs. I want to plot them in a bar graph with the specific dates in the x-axis.

我有一个由日期值对组成的数据集。我想用 x 轴中的特定日期将它们绘制在条形图中。

My problem is that matplotlibdistributes the xticksover the entire date range; and also plots the data using points.

我的问题是在整个日期范围内matplotlib分布xticks；并使用点绘制数据。

The dates are all datetimeobjects. Here's a sample of the dataset:

日期都是datetime对象。这是数据集的示例：

data = [(DT.datetime.strptime('2010-02-05', "%Y-%m-%d"), 123),
        (DT.datetime.strptime('2010-02-19', "%Y-%m-%d"), 678),
        (DT.datetime.strptime('2010-03-05', "%Y-%m-%d"), 987),
        (DT.datetime.strptime('2010-03-19', "%Y-%m-%d"), 345)]

Here is a runnable code sample using pyplot

这是一个可运行的代码示例，使用 pyplot

import datetime as DT
from matplotlib import pyplot as plt

data = [(DT.datetime.strptime('2010-02-05', "%Y-%m-%d"), 123),
        (DT.datetime.strptime('2010-02-19', "%Y-%m-%d"), 678),
        (DT.datetime.strptime('2010-03-05', "%Y-%m-%d"), 987),
        (DT.datetime.strptime('2010-03-19', "%Y-%m-%d"), 345)]

x = [date for (date, value) in data]
y = [value for (date, value) in data]

fig = plt.figure()

graph = fig.add_subplot(111)
graph.plot_date(x,y)

plt.show()

QUESTION SUMMARY:
My situation is more like I have an Axesinstance ready (referenced by graphin the code above) and I want to do the following:

问题摘要：
我的情况更像是我Axes准备好了一个实例（graph在上面的代码中引用），我想做以下事情：

1. Make the xtickscorrespond to the exact date values. I have heard of matplotlib.dates.DateLocatorbut I have no idea how create one and then associate it with a specific Axesobject.
2. Get tighter control over the type of graph being used (bar, line, points, etc.)

1. 使xticks对应于确切的日期值。我听说过，matplotlib.dates.DateLocator但我不知道如何创建一个，然后将其与特定Axes对象相关联。
2. 更严格地控​​制所使用的图形类型（条形、线形、点等）

采纳答案by Joe Kington

What you're doing is simple enough that it's easiest to just using plot, rather than plot_date. plot_date is great for more complex cases, but setting up what you need can be easily accomplished without it.

你正在做的事情很简单，只使用 plot 而不是 plot_date 是最简单的。plot_date 非常适合更复杂的情况，但没有它也可以轻松完成设置所需的内容。

e.g., Based on your example above:

例如，基于你上面的例子：

import datetime as DT
from matplotlib import pyplot as plt
from matplotlib.dates import date2num

data = [(DT.datetime.strptime('2010-02-05', "%Y-%m-%d"), 123),
        (DT.datetime.strptime('2010-02-19', "%Y-%m-%d"), 678),
        (DT.datetime.strptime('2010-03-05', "%Y-%m-%d"), 987),
        (DT.datetime.strptime('2010-03-19', "%Y-%m-%d"), 345)]

x = [date2num(date) for (date, value) in data]
y = [value for (date, value) in data]

fig = plt.figure()

graph = fig.add_subplot(111)

# Plot the data as a red line with round markers
graph.plot(x,y,'r-o')

# Set the xtick locations to correspond to just the dates you entered.
graph.set_xticks(x)

# Set the xtick labels to correspond to just the dates you entered.
graph.set_xticklabels(
        [date.strftime("%Y-%m-%d") for (date, value) in data]
        )

plt.show()

If you'd prefer a bar plot, just use plt.bar(). To understand how to set the line and marker styles, see plt.plot()Plot with date labels at marker locations http://www.geology.wisc.edu/~jkington/matplotlib_date_labels.png

如果您更喜欢条形图，只需使用plt.bar(). 要了解如何设置线条和标记样式，请参阅在标记位置使用日期标签绘图 http://www.geology.wisc.edu/~jkington/matplotlib_date_labels.pngplt.plot()