Arrow on a line plot with matplotlib

Question

I'd like to add an arrow to a line plot with matplotlib like in the plot below (drawn with pgfplots).

How can I do (position and direction of the arrow should be parameters ideally)?

Here is some code to experiment.

from matplotlib import pyplot import numpy as np  t = np.linspace(-2, 2, 100) plt.plot(t, np.sin(t)) plt.show() 

Thanks.

Answer 1

In my experience this works best by using annotate. Thereby you avoid the weird warping you get with ax.arrow which is somehow hard to control.

EDIT: I've wrapped it into a little function.

from matplotlib import pyplot as plt import numpy as np   def add_arrow(line, position=None, direction='right', size=15, color=None):     """     add an arrow to a line.      line:       Line2D object     position:   x-position of the arrow. If None, mean of xdata is taken     direction:  'left' or 'right'     size:       size of the arrow in fontsize points     color:      if None, line color is taken.     """     if color is None:         color = line.get_color()      xdata = line.get_xdata()     ydata = line.get_ydata()      if position is None:         position = xdata.mean()     # find closest index     start_ind = np.argmin(np.absolute(xdata - position))     if direction == 'right':         end_ind = start_ind + 1     else:         end_ind = start_ind - 1      line.axes.annotate('',         xytext=(xdata[start_ind], ydata[start_ind]),         xy=(xdata[end_ind], ydata[end_ind]),         arrowprops=dict(arrowstyle="->", color=color),         size=size     )   t = np.linspace(-2, 2, 100) y = np.sin(t) # return the handle of the line line = plt.plot(t, y)[0]  add_arrow(line)  plt.show() 

It's not very intuitive but it works. You can then fiddle with the arrowprops dictionary until it looks right.