On 9/27/13 6:22 PM, Tim Chase wrote:
I've got a large heapq'ified list and want to walk it in-order without altering it. I get the "unsorted" heap'ish results if I just dofrom heapq import heappush, heappop, nlargest, nsmallest my_heap = [] for thing in lots_of_items(): heappush(thing) for item in my_heap: ... To get them in-order, I can do something like while my_heap: item = heappop(my_heap) do_something(item) to iterate over the items in order, but that destroys the original heap. I can also do for item in nlargest(len(my_heap), my_heap): # or nsmallest() do_something(item) but this duplicates a potentially large list according to my reading of the description for nlargest/nsmallest[1]. Is there a handy way to non-destructively walk the heap (either in-order or reversed) without duplicating its contents?
If you add all your items at once, and then you want to walk over all the items, then don't use a heap. Just put all your items in a list, and then sort it. The advantage of a heap is that you can add items to it with little effort, delaying some of the work until when you need to get the items out. It maintains a partially-sorted list that's good for insertion and popping. You have different needs. Use a sorted list.
--Ned.
-tkc [1] http://docs.python.org/2/library/heapq.html#heapq.nlargest
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