[Tutor] Graphing the random.gauss distribution

[Kent Johnson]

Dick Moores wrote:
> Kent Johnson posted this to Tutor list Aug 8, 2007 
> (<http://mail.python.org/pipermail/tutor/2007-August/056194.html>):
> 
> ============================================
>  > Python provides you with a pseudo random number generator whose output
>  > values are uniformly distributed between the input parameters.  What you
>  > are dealing with in fish weights or test scores or other natural
>  > phenomena is most likely a normal distribution. Check out Wikipedia's
>  > normal distribution entry.  The math is really juicy. You may end up
>  > with a recipe for the Python Cookbook.
> 
> No need for all that, use random.gauss()
> 
> Kent
> ============================================
> 
> I hadn't noticed gauss was there in the Random module. I got to 
> wondering if I could graph the distribution. This code produces a 
> nice bell-curve-seeming curve (on its side). Takes about 80 secs to 
> run on my computer. To fit your situation, the length of the bars can 
> be shortened or lengthened by decreasing or increasing, respectively, 
> the divisor of gaussCalls in line 5, "barLengthAdjuster = gaussCalls//2600".
> 
> Dick Moores
> 
> ==============================
> from random import gauss
> mean = 100
> std = 10
> gaussCalls = 10000000
> barLengthAdjuster = gaussCalls//2600
> 
> d = []
> for k in range(200):
>      d.append([k, 0])

This could be a list comprehension:
d = [ [k, 0] for k in range(200) ]
but there is no need to keep the array index in the array so this is 
simpler:

d = [0] * 200

> for k in xrange(gaussCalls):
>      n = int(gauss(mean, std))
>      d[n][1] += 1

This becomes just
      d[n] += 1

> 
> for c in d:
>      barLength = c[1]//barLengthAdjuster
>      print barLength, "=", c[0], c[1]

Use enumerate() to get the indices as well as the list contents. This 
version prints an actual bar as well:
for i, count in enumerate(d):
      barLength = count//barLengthAdjuster
      print i, '*' * barLength, count

Kent