Harmonic mean in a python function?

Question

I have 2 functions that give out precision and recall scores, I need to make a harmonic mean function defined in the same library that uses these two scores. The functions looks like this:

here are the functions:

def precision(ref, hyp):
    """Calculates precision.
    Args:
    - ref: a list of 0's and 1's extracted from a reference file
    - hyp: a list of 0's and 1's extracted from a hypothesis file
    Returns:
    - A floating point number indicating the precision of the hypothesis
    """
    (n, np, ntp) = (len(ref), 0.0, 0.0)
    for i in range(n):
            if bool(hyp[i]):
                    np += 1
                    if bool(ref[i]):
                            ntp += 1
    return ntp/np

def recall(ref, hyp):
    """Calculates recall.
    Args:
    - ref: a list of 0's and 1's extracted from a reference file
    - hyp: a list of 0's and 1's extracted from a hypothesis file
    Returns:
    - A floating point number indicating the recall rate of the hypothesis
    """
    (n, nt, ntp) = (len(ref), 0.0, 0.0)
    for i in range(n):
            if bool(ref[i]):
                    nt += 1
                    if bool(hyp[i]):
                            ntp += 1
    return ntp/nt

What would the harmonic mean function look like? All I have is this but I know its not right:

def F1(precision, recall):
    (2*precision*recall)/(precision+recall)

Answer 1

With a slight change of your F1 function, and with the same precision and recall function you defined, I have this working:

def F1(precision, recall):
    return (2*precision*recall)/(precision+recall)

r = [0,1,0,0,0,1,1,0,1]
h = [0,1,1,1,0,0,1,0,1]
p = precision(r, h)
rec = recall(r, h)
f = F1(p, rec)
print f

Review especially the use of variables I have. You must compute the result of each function and pass them to the F1 function.

Answer 2

The following will work with any number of arguments:

def hmean(*args):
    return len(args) / sum(1. / val for val in args)

To compute the harmonic mean of precision and recall, use:

result = hmean(precision, recall)

There are two problems with your function:

1. It fails to return a value.
2. On some versions of Python, it would use integer division for integer arguments, truncating the result.