Need help on finding AVERAGE in python

Question

What is the average value of the numbers in the field [quant] in the range (198) and (272) inclusive

this is the code that i tried. Above is the [quant] field from where i need to find the average.

word_file = open('300000a.csv','r')

firstLine = True 
for line in word_file:
    if firstLine:
        firstLine = False
        continue
    line = line.strip()
    line = line.split (",")
    field = int(line[0])

TotalMetalCount +=1
if  field >198 or field <272:
  metalCounts += 1
else:
    metalCounts = 1


countT +=1
if field >198 or field <272:
        count += 1

[`reduce(lambda x, y: x + y, l) / len(l)`](http://stackoverflow.com/questions/9039961/finding-the-average-of-a-list) — Grijesh Chauhan, May 14 '13 at 12:23
@GrijeshChauhan Please don't suggest `reduce` when you can just use `sum` — jamylak, May 14 '13 at 12:25
@LevLevitsky yeah... not quite sure why it's been asked again. Anyway, it must be part of a class/assignment, but http://stackoverflow.com/questions/16522767/need-help-on-average-python asked it much better - so would suggest to the OP to read that one... — Jon Clements, May 14 '13 at 12:36
I have read your code some times, but I don't known what is the meaning of your code and the variable. — Tanky Woo, May 14 '13 at 12:41
The same user has already asked this question, only with minor differences: http://stackoverflow.com/questions/16486849/finding-average-value-of-numbers-in-range-298-272 — timss, May 14 '13 at 13:34

eandersson · Answer 1 · 2013-05-14T14:08:54.690

2

You can calculate the average of a list using sum and dividing it by the length.

float(sum(my_list))/len(my_list)

If you need to grab only a few specific items and extract the average based on those you can slice the array.

print(float(sum(my_list[198:272]))/len(my_list[198:272]))

If you have a list that contains strings, and not integers you need to convert them to a list of integers before you can use sum.

my_list_of_integers = [int(i) for i in my_list[198:272]
print(float(sum(my_list_of_integers))/len(my_list_of_integers]))

edited May 14 '13 at 14:08

answered May 14 '13 at 12:26

eandersson

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Looks like, @user2370772 need to take not all elements but only part of them. So filtering list will explanation will be good for him – cleg May 14 '13 at 12:27
Ah. Yea, that is probably true. – eandersson May 14 '13 at 12:28
i tried the second code and it comes up with "error" "invalid syntax" and it showing me INT in red... what should i do – user2370772 May 14 '13 at 13:09
I updated the example in case you use Python3. – eandersson May 14 '13 at 14:09
@eandersson, the sum will behave badly in Python2 because it (probably) does an integer division. Safer to convert both to float individually. – Adrian Ratnapala May 14 '13 at 14:16
@AdrianRatnapala True, for sure the safest, but I tested it in Python 2.7.3. – eandersson May 14 '13 at 14:21
In python 2.7.3 `2/3 == 0`. I think if you divide two sums of ints you will be in trouble unless you use some kind of `__future__` import. – Adrian Ratnapala May 14 '13 at 14:45

score 0 · Answer 2 · answered May 14 '13 at 14:14

If you are going to be doing much more numerics than this, you should use numpy. Then there will be various ways of reading CSV files as arrays. Those arrays have a .mean() method, which does what you think it does.

(But if you don't do more numerics, then @eandersson answer is more proportionate).

Need help on finding AVERAGE in python

2 Answers2