How do I get my Median Program to work (part 2)

Question

I am trying to make a median program. This is my code.

def median(list=[]):
    x = 0
    list = sorted(list)
    if len(list) % 2 == 0:
        b = int((len(list)/2))
        print b
        c = int(len(list)/2)
        x = [list[b-1],list[c]]
        print x
        x = float((x[0]+x[1])/2)
        print str(x)
    else:
        print list[((len(list)//2))]

When I run it, I get this

>>> median([1,2,3,4])
2
[2, 3]
2.0

What is happening?

Please note: I do not want any advice on ways to do it better, I just want help.

I'm not sure. I use Pythonista. Does it matter? – Midataur Nov 30 '15 at 04:23 — Midataur, Nov 30 '15 at 04:23
I think Pythonista uses Python 2.7.4 – Midataur Nov 30 '15 at 04:24 — Midataur, Nov 30 '15 at 04:24
Yes, it does. Please, show the result of `3 / 2`. – awesoon Nov 30 '15 at 04:25 — awesoon, Nov 30 '15 at 04:25
It returns 1 when 1 type 3 / 2 – Midataur Nov 30 '15 at 04:28 — Midataur, Nov 30 '15 at 04:28
Thanks @soon I will try this – Midataur Nov 30 '15 at 04:29 — Midataur, Nov 30 '15 at 04:29

Ryan · Answer 1 · 2015-11-30T04:29:27.683

Python 3.4 has statistics.median

Here is a example of how to use it

import statistics

values = [1, 2, 3, 6, 8]

print(statistics.median(values))

If you don't use python version 3.4 you could always right a function like this one i have included

def median(lst):
    lst = sorted(lst)
    if len(lst) < 1:
            return None
    if len(lst) %2 == 1:
           return lst[((len(lst)+1)/2)-1]
    else:
            return float(sum(lst[(len(lst)/2)-1:(len(lst)/2)+1]))/2.0

while these may be the more pythonic way to do it, if you would like your specific function, you can do it like this

def median(list=[]):
    x = 0
    list = sorted(list)
    if len(list) % 2 == 0:
        b = int((len(list)/2.0))
        print b
         c = int(len(list)/2.0)
        x = [list[b-1],list[c]]
        print x
        x = float((x[0]+x[1])/2.0)
        print str(x)
    else:
        print list[((len(list)//2.0))]

median([1,2,3,4])

I want to write my own function. I am not asking for how to do it better, I am asking why I am getting this result — Midataur, Nov 30 '15 at 04:25

score 1 · Answer 2 · answered Nov 30 '15 at 04:27

Try this, look for 2.0 instead of 2 on division

def median(list=[]):
    x = 0
    list = sorted(list)
    if len(list) % 2 == 0:
        b = int((len(list)/2.0))
        print b
        c = int(len(list)/2.0)
        x = [list[b-1],list[c]]
        print x
        x = float((x[0]+x[1])/2.0)
        print str(x)
    else:
        print list[((len(list)//2))]

Simon · Answer 3 · 2015-11-30T05:27:14.970

You should cast the elements of x to a float before taking the average:

def median(list=[]):
    x = 0
    list = sorted(list)
    if len(list) % 2 == 0:
        b = int(len(list)/2)
        print b
        c = int(len(list)/2)
        x = [list[b-1],list[c]]
        print x
        x = (float(x[0])+float(x[1]))/2
        print str(x)
    else:
        print list[((len(list)//2))]

median([1,2,3,4])

In the original you had x = float((x[0]+x[1])/2). So that's adding 2 integers and dividing them. If this is python 2 the you run into the integer division problem (I don't believe this will happen in python 3 because / is float division by default). You fix this by explicitly telling python that your values are floats (as I did above), or you can from __future__ import division and just use the default float division from python 3.

Also, b and c are both set to the same value so you don't need to store them both separately. Just use either b or c when calculating your list x

How do I get my Median Program to work (part 2)

3 Answers3