My professor wrote this median function and I don't understand it very well. Can someone please explain the part about i = len(list)/2 and median = avg() and the else statement?
def avg_list(numbers):
sum = 0
for num in numbers:
sum += num
avg = float(sum)/len(numbers)
print avg
def median(list):
list.sort()
if len(list)%2 == 0:
#have to take avg of middle two
i = len(list)/2
median = avg()
else:
#find the middle (remembering that lists start at 0)
i = len(list)/2
median = list
return median
To add from an example I saw, for even list length:
def median(s):
i = len(s)
if not i%2:
return (s[(i/2)-1]+s[i/2])/2.0
return s[i/2]
This works very well but I don't understand the last return s[i/2]?
For odd list length:
x = [1,2,5,2,3,763,234,23,1,234,21,3,2134,23,54]
median = sorted(x)[len(x)/2]
Since x has a list length of odd, wouldn't the [len(x)/2] be a floating number index? I'm not getting this all the way? Any explanation better than mine is much appreciated.
We're missing some code here, but we can puzzle it out.
The comments here are instructive. When we check:
if len(list)%2 == 0:
Then we're checking to see if the list is of even length. If a list has an even number of members, then there is no true "middle" element, and so:
#have to take avg of middle two
i = len(list)/2
median = avg()
We assume that the avg() function is going to return the average of the two middle elements. Since you didn't include a definition of an avg function, it's possible that this is really supposed to be an avg_list function taking the middle two elements of the list.
Now, if the list is of odd length, there is a middle element, and so:
else:
#find the middle (remembering that lists start at 0)
i = len(list)/2
median = list
Now this looks kinda wrong to me too, but my guess is that the intention is that this should read:
median = list[i]
That would be us returning the middle element of the list. Since the list has been sorted, that middle element is the true median of the list.
Hope this helps!