Question

I’m new to Python and have a list of numbers. e.g.
5,10,32,35,64,76,23,53....

and I’ve grouped them into fours (5,10,32,35, 64,76,23,53 etc..) using the code from this post.

def group_iter(iterator, n=2, strict=False):
    """ Transforms a sequence of values into a sequence of n-tuples.
    e.g. [1, 2, 3, 4, ...] => [(1, 2), (3, 4), ...] (when n == 2)
    If strict, then it will raise ValueError if there is a group of fewer
    than n items at the end of the sequence. """
    accumulator = []
    for item in iterator:
        accumulator.append(item)
        if len(accumulator) == n: # tested as fast as separate counter
            yield tuple(accumulator)
            accumulator = [] # tested faster than accumulator[:] = []
            # and tested as fast as re-using one list object
    if strict and len(accumulator) != 0:
        raise ValueError("Leftover values")

How can I access the individual arrays so that I can perform functions on them. For example, I’d like to get the average of the first values of every group (e.g. 5 and 64 in my example numbers).

Answer 1

Let’s say you have the following tuple of tuples:

a=((5,10,32,35), (64,76,23,53)) 

To access the first element of each tuple, use a for-loop:

for i in a:
     print i[0]

To calculate average for the first values:

elements=[i[0] for i in a]

avg=sum(elements)/float(len(elements))