绘制水平线（matplotlib）

Question

我尝试运行代码：

fig, ax = plt.subplots()
ax.plot(x, y, color="g") 
ax.xaxis.set_major_locator(matplotlib.dates.YearLocator())
ax.xaxis.set_major_formatter(matplotlib.dates.DateFormatter('%Y'))
hlines=[40,50]
ax.hlines(hlines, 1, len(x), color='g')
plt.show()

我希望它能画出这样的东西： 画图表没问题，可以，但是画水平线不行。

当我运行我的代码时，它会绘制：

PS x 是这样创建的：日期到 matplotlib 日期

x.append(matplotlib.dates.date2num(datetime.strptime(date, '%Y%m%d')))

Answer 1

You are drawing a horizontal line from x-axis=1 to x-axis=len(x), which are just arbitrary integers that does not represent anything on your graph: your x-axis is much larger because you use matplotlib.dates.date2num. You need to properly assign the range for your horizontal line. For example:

ax.hlines(hlines, min(x), max(x), color='g')

or

ax.hlines(hlines,
          matplotlib.dates.date2num(datetime.strptime(mindate, '%Y%m%d')),
          matplotlib.dates.date2num(datetime.strptime(maxdate, '%Y%m%d')),
          color='g')

or you could just use axhline:

ax.axhline(40, color='g')
ax.axhline(50, color='g')