[Matplotlib] Ploting an exponential distribution frequency curve

Mario Figueiredo marfig at gmail.com
Sun Apr 26 00:33:10 CEST 2015


I'm trying to plot the curve of an exponential distribution without
much success. I'm missing something very basic I feel, but just can't
figure it out after numerous tries, so I'm turning out to you.

This is the function generating the frequency of individual outcomes:

    import decimal
    from random import expovariate
    from collections import defaultdict

    decimal.getcontext().prec = 4
    Dec = decimal.Decimal

    samples = 100000   # 100,000

    def generate(lambd):
        res = defaultdict(int)
        for _ in range(samples):
            res[Dec(expovariate(lambd)).quantize(Dec('0.01'))] += 1
        return res

Trying to plot this data into a frequency curve is proving too
challenging and I just can't understand why.

    plot(list(results.keys()), list(results.values()))

This results in strange line graph where there is the outline of an
exponential curve but the line crisscrosses all over the place. I
can't understand why I am getting this graph result and not just the
smooth line I can infer from looking at the hard data.



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