Question

Working in Python 2.7.

I’m trying to plot a histogram for the numbers generated by 50 run-throughs of my random walk. But when I use pylab.hist(batting_average, bins = 10), I get a weird multi-colored histogram that goes up close to 500, but with only 50 runs of the walk, the maximum it should be able to go on the y-axis would be 50.

Here’s my code:

a = ['Hit', 'Out']
b = [.3, .7]


def battingAverage(atBats, some_list=a, probabilities=b):
    num_hits = 0
    num_outs = 0
    current_BA = []
    for i in range(1,atBats):
        if random_pick(a, b) == 'Hit':
            num_hits += 1
        else:
            num_outs +=1
        BA = float(num_hits)/(float(num_hits)+float(num_outs))
        current_BA.append(BA)
    return current_BA

def printBAs():
    for i in range(50):
        batting_average = battingAverage(501)
        pylab.hist(batting_average, bins=10)

What’s wrong with my histogram!?

Let me know if anything needs clarification, and I’ll do my best.

Answer 1

The argument passed to battingAverage is 501… and is the number of at-bats. You’re doing 50 histograms with 500 at-bats per histogram.

(Oh, and you need to fix the formatting of your code… the indentation is messed up.)

Your code doesn’t do what you think it does.

I think you’re wanting battingAverage to return the final batting average, but it returns a list of batting averages, one for each at-bat.
Then you’re plotting that list.

I think you want to return a single number from battingAverage, and you want to accumulate the list in the printBAs() function, and move pylab.hist out of the for loop.

I don’t suppose this is homework?

In other words, I think you want something like this:

a = ['Hit', 'Out']
b = [.3, .7]

def battingAverage(atBats, results=a, probabilities=b):
    num_hits = 0
    num_outs = 0
    for i in range(atBats):
        if random_pick(results, probabilities) == 'Hit':
            num_hits += 1
        else:
            num_outs +=1
    BA = float(num_hits)/(float(num_hits)+float(num_outs))
    return BA

def printBAs():
    batting_averages = [battingAverage(500) for i in range(50)]
    pylab.hist(batting_averages, bins=10)

Though that code still needs cleanup…