How to break down a python list

[ronparker]

Hello all!

I have a variable name "thelist" which is a list of 100,000 elements. I was wondering how I can make two new lists of the average value and standard deviation from this. For example if my list is [1,2,3,4,5,6,7,8 ,9,10] then the new list would be the average of the every 5 numbers, endeing up looking like [average(1,2,3,4 ,5),average(6,7 ,8,9,10)]=[3,8]. I am very comfortable using numpy to get the average and standard deviation values. I am just having trouble breaking the initial list down. I'm not sure if this is what indexing is.

Any help would really be appreciated,
Thank YOU!

[ronparker]

I am also curious to know if there is a simple way to see how many positive numbers there are in each 100 segments of the bit 100,000 list. Thank YOU!

[dwblas]

For example if my list is [1,2,3,4,5,6,7,8 ,9,10] then the new list would be the average of the every 5 numbers

You can use two for loops. With the outer loop, set the step value at 5 or whatever the increment. The inner loop adds each of the 5 numbers together.

test_list = range(1, 51)
for outer in range(0, len(test_list), 5):
    total = 0
    for inner in range(5):
        total += test_list[outer+inner]
        print test_list[outer+inner],
    print "\n", float(total)/5

[Andrew Grigorev]

omg, awful!

lambda lst, ln: [ lst[i:i+ln] for i in range(0, len(lst), ln) ]

[bvdet]

What's the lambda for?

>>> data = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]
>>> n = 5
>>> def average(seq):
... 	return sum(seq)/float(len(seq))
... 
>>> [average(data[i:i+n]) for i in range(0, len(data), n)]
[3.0, 8.0, 13.0]
>>> data = [1,2,-3,4,5,6,-7,8,-9,10,11,-12,-13,-14,15]
>>> [sum([1 for item in data[i:i+n] if item>0]) for i in range(0, len(data), n)]
[4, 3, 2]
>>>