Question

I’m plotting line graphs in Python Matplotlib of times which I get in mm:ss.tttt format.

I’ve already converted the values back to 10thousanths of a second and I can create a nice plot. But that means the Y axis show a value of “832323” instead of easier to read “1:23.2323”.

Is there some way I can format the output values appropriately?

Answer 1

I worked this out myself shortly after I wrote this. Use Matplotlibs’s axis, set_major_formatter() function.

I wrote a quick formatting function that would take a value in 10-thousandths of a second and turn it back into mm:ss.tttt. And then passed this formatter to the axis definition.

Import the ‘ticker’ module along with the plotting stuff:

import matplotlib.pyplot as plt                                                 
from matplotlib import ticker  

Create your own value formatting function:

def format_10Kth_time(time, pos=None):                                          
    mins     = time // (10000 * 60)                                             
    secs     = (time - (mins * 10000 * 60)) // (10000)                          
    fracsecs = time % 10000                                                     
    return "%d:%02d.%d" % (mins, secs, fracsecs)

Then in my plot code I did this to alter the Y axis formatting:

plt.gca().yaxis.set_major_formatter(ticker.FuncFormatter(format_10Kth_time))
plt.plot(...) 
plt.show()