Finding the average of a list
Finding the average of a list
Question
I have to find the average of a list in Python. This is my code so far
l = [15, 18, 2, 36, 12, 78, 5, 6, 9]
print reduce(lambda x, y: x + y, l)
I've got it so it adds together the values in the list, but I don't know how to make it divide into them?
Accepted Answer
On Python 3.4+ you can use statistics.mean()
l = [15, 18, 2, 36, 12, 78, 5, 6, 9]
import statistics
statistics.mean(l) # 20.11111111111111
On older versions of Python you can do
sum(l) / len(l)
On Python 2 you need to convert len to a float to get float division
sum(l) / float(len(l))
There is no need to use reduce. It is much slower and was removed in Python 3.
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You can use numpy.mean:
l = [15, 18, 2, 36, 12, 78, 5, 6, 9]
import numpy as np
print(np.mean(l))
A statistics module has been added to python 3.4. It has a function to calculate the average called mean. An example with the list you provided would be:
from statistics import mean
l = [15, 18, 2, 36, 12, 78, 5, 6, 9]
mean(l)
Why would you use reduce() for this when Python has a perfectly cromulent sum() function?
print sum(l) / float(len(l))
(The float() is necessary to force Python to do a floating-point division.)
There is a statistics library if you are using python >= 3.4
https://docs.python.org/3/library/statistics.html
You may use it's mean method like this. Let's say you have a list of numbers of which you want to find mean:-
list = [11, 13, 12, 15, 17]
import statistics as s
s.mean(list)
It has other methods too like stdev, variance, mode, harmonic mean, median etc which are too useful.
Instead of casting to float, you can add 0.0 to the sum:
def avg(l):
return sum(l, 0.0) / len(l)