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Lowest Value in List

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Dear Group,

I am trying to work out a solution to the following problem in Python. 

The Problem:
Suppose I have three lists.
Each list is having 10 elements in ascending order.
I have to construct one list having 10 elements which are of the lowest value among these 30 elements present in the three given lists.

The Solution:

I tried to address the issue in the following ways:

a) I took three lists, like,
list1=[1,2,3,4,5,6,7,8,9,10]
list2=[0,1,2,3,4,5,6,7,8,9]
list3=[-5,-4,-3,-2,-1,0,1,2,3,4]

I tried to make sum and convert them as set to drop the repeating elements:
set_sum=set(list1+list2+list3)
set([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, -1, -5, -4, -3, -2])

In the next step I tried to convert it back to list as,
list_set=list(set_sum)
gave the value as,
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, -1, -5, -4, -3, -2]

Now, I imported heapq as, 
import heapq

and took the result as,
result=heapq.nsmallest(10,list_set)
it gave as,
[-5, -4, -3, -2, -1, 0, 1, 2, 3, 4]

b) I am thinking to work out another approach.
I am taking the lists again as,

list1=[1,2,3,4,5,6,7,8,9,10]
list2=[0,1,2,3,4,5,6,7,8,9]
list3=[-5,-4,-3,-2,-1,0,1,2,3,4]

as they are in ascending order, I am trying to take first four/five elements of each list,like,

list1_4=list1[:4]
>>> list2_4=list2[:4]
>>> list3_4=list3[:4]

Now, I am trying to add them as,

list11=list1_4+list2_4+list3_4

thus, giving us the result

[1, 2, 3, 4, 0, 1, 2, 3, -5, -4, -3, -2]

Now, we are trying to sort the list of the set of the sum as,

sort_sum=sorted(list(set(list11)))

giving us the required result as,

[-5, -4, -3, -2, 0, 1, 2, 3, 4]

If by taking the value of each list portion as 4 gives as less number of elements in final value, as we are making set to avoid repeating numbers, we increase element count by one or two and if final result becomes more than 10 we take first ten.

Are these approaches fine. Or should we think some other way.

If any learned member of the group can kindly let me know how to solve I would be helpful enough.

Thanking in Advance,
Subhabrata. 

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Lowest Value in List subhabangalore@gmail.com - 2013-10-02 03:04 -0700
  Re: Lowest Value in List Steven D'Aprano <steve@pearwood.info> - 2013-10-02 10:10 +0000
  Re: Lowest Value in List Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2013-10-02 12:42 +0200
  Re: Lowest Value in List dvghana@gmail.com - 2013-10-02 05:56 -0700
  Re: Lowest Value in List Ravi Sahni <ganeshsahni07@gmail.com> - 2013-10-02 19:35 +0530
  Re: Lowest Value in List Peter Otten <__peter__@web.de> - 2013-10-03 13:12 +0200

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