如何在Pyplot注释中设置有效数字

Question

P-values and D-Values from a KS test need to be displayed on a pylot histogram. Thankfully, my p-values are low, but are so low they display as 0.0 when I use round . I also tried numpy.set_printoptions(precision=3) to limit my significant digits to the thousands place, but this only changed my output printing to the interpreter, and not to the graph.

 ks_D, ks_p = ks_2samp(cntrl, test)

 ks_summ = "K-S D-value = {}\nK-S p-value = {}".format(round(ks_D, 3), round(ks_p, 3))
pyplot.annotate(ks_summ, xy=(0.70, 0.75), xycoords='axes fraction')

So how can I display 1.2228387401e-24 ( <class 'numpy.float64'> ) as 1.223e-24 in a graph annotation?

Here is my graph with p-value showing as 0.0:

Answer 1

You need modify the line

ks_summ = "K-S D-value = {}\nK-S p-value = {}".format(round(ks_D, 3), round(ks_p, 3))

to read

ks_summ = "K-S D-value = {}\nK-S p-value = {:.3e}".format(round(ks_D, 3), ks_p)

The {:.3e} format means 3 decimal places with exponential notation. And since the rounding to 3 decimal places in included in this formatting notation, we can drop the code to round ks_p . For example:

>>> ks_p = 1.2228387401e-24
>>> '{:.3e}'.format(ks_p)
'1.223e-24'

Finally, note that you can apply a string format to ks_D , as well. Something {:.3f} may do the trick (ie three decimal place rounding).

>>> ks_D = 0.38210101
>>> '{:.3f}'.format(ks_D)
'0.382'