Adding an arbitrary line to a matplotlib plot in ipython notebook

Question

I m rather new to both python matplotlib and using it through the ipython notebook  I m trying to add some annotation lines to an existing graph and I can t figure out how to render the lines on a graph  So  for example  if I plot the following   import numpy as np np random seed 5  x   arange 1  101  y   20   3   x   np random normal 0  60  100  p    plot x  y   o     I get the following graph     So how would I add a vertical line from  70 100  up to  70 250   What about a diagonal line from  70 100  to  90 200    I ve tried a few things with Line2D   resulting in nothing but confusion on my part  In R I would simply use the segments   function which would add line segments  Is there an equivalent in matplotlib

User · Answer

Using vlines   import numpy as np np random seed 5  x   arange 1  101  y   20   3   x   np random normal 0  60  100  p    plot x  y   o   vlines 70 100 250    The basic call signatures are   vlines x  ymin  ymax  hlines y  xmin  xmax

User · Answer

It s not too late for the newcomers    plt axvline x  color  r     It takes the range of y as well  using ymin and ymax

User · Answer

Rather than abusing plot or annotate  which will be inefficient for many lines  you can use matplotlib collections LineCollection   import numpy as np import matplotlib pyplot as plt from matplotlib collections import LineCollection  np random seed 5  x   np arange 1  101  y   20   3   x   np random normal 0  60  100  plt plot x  y   o      Takes list of lines  where each line is a sequence of coordinates l1     70  100    70  250   l2     70  90    90  200   lc   LineCollection  l1  l2   color   k   blue    lw 2   plt gca   add collection lc   plt show       It takes a list of lines  l1  l2        where each line is a sequence of N coordinates  N can be more than two    The standard formatting keywords are available  accepting either a single value  in which case the value applies to every line  or a sequence of M values  in which case the value for the ith line is values i   M

User · Answer

You can directly plot the lines you want by feeding the plot command with the corresponding data  boundaries of the segments    plot  x1  x2    y1  y2   color  k   linestyle  -   linewidth 2    of course you can choose the color  line width  line style  etc    From your example   import numpy as np import matplotlib pyplot as plt  np random seed 5  x   np arange 1  101  y   20   3   x   np random normal 0  60  100  plt plot x  y   o       draw vertical line from  70 100  to  70  250  plt plot  70  70    100  250    k-   lw 2     draw diagonal line from  70  90  to  90  200  plt plot  70  90    90  200    k-    plt show

User · Answer

Matplolib now allows for  annotation lines  as the OP was seeking  The annotate   function allows several forms of connecting paths and a headless and tailess arrow  i e   a simple line  is one of them    ax annotate                 xy  0 2  0 2   xycoords  data               xytext  0 8  0 8   textcoords  data               arrowprops dict arrowstyle  -                         connectionstyle  arc3  rad 0                    In the documentation it says you can draw only an arrow with an empty string as the first argument   From the OP s example    matplotlib notebook import numpy as np import matplotlib pyplot as plt  np random seed 5  x   np arange 1  101  y   20   3   x   np random normal 0  60  100  plt plot x  y   o       draw vertical line from  70 100  to  70  250  plt annotate                   xy  70  100   xycoords  data                 xytext  70  250   textcoords  data                 arrowprops dict arrowstyle  -                                 connectionstyle  arc3 rad 0                         draw diagonal line from  70  90  to  90  200  plt annotate                   xy  70  90   xycoords  data                 xytext  90  200   textcoords  data                 arrowprops dict arrowstyle  -                                 connectionstyle  arc3 rad 0                       plt show       Just as in the approach in gcalmettes s answer  you can choose the color  line width  line style  etc     Here is an alteration to a portion of the code that would make one of the two example lines red  wider  and not 100  opaque     draw vertical line from  70 100  to  70  250  plt annotate                   xy  70  100   xycoords  data                 xytext  70  250   textcoords  data                 arrowprops dict arrowstyle  -                                 edgecolor    red                                 linewidth 5                                alpha 0 65                                connectionstyle  arc3 rad 0                        You can also add curve to the connecting line by adjusting the connectionstyle

[matplotlib] Adding an arbitrary line to a matplotlib plot in ipython notebook

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