The two sequences are pairs and have to be sorted as such. There are in fact hundreds of thousands of pairs of sequences (with different elements) with each sequence containing 10,000+ elements.
Looks like pairs = sorted(zip(g,h)) is the best option? Dinesh Message: 6 Date: Sat, 12 Mar 2011 11:16:30 +1100 From: Steven D'Aprano <st...@pearwood.info> To: tutor@python.org Subject: Re: [Tutor] Sorting multiple sequences Message-ID: <4d7abb5e.9080...@pearwood.info> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Dinesh B Vadhia wrote: > I want to sort two sequences with different data types but both with an equal > number of elements eg. > > f = [0.21, 0.68, 0.44, ..., 0.23] > i = [6, 18, 3, ..., 45] > > The obvious solution is to use zip ie. pairs = zip(f,i) followed by > pairs.sort(). This is fine It doesn't sound fine to me. Sorting pairs of items is *not* the same as sorting each sequence separately, except by accident. Even with the small example shown, you can see this: >>> f = [0.21, 0.68, 0.44, 0.23] >>> i = [6, 18, 3, 45] >>> sorted(f); sorted(i) # sorting individually [0.21, 0.23, 0.44, 0.68] [3, 6, 18, 45] >>> pairs = sorted(zip(f, i)) # sorting as pairs >>> print(pairs) [(0.21, 6), (0.23, 45), (0.44, 3), (0.68, 18)] >>> list(zip(*pairs)) # Split the pairs into separate sequences. [(0.21, 0.23, 0.44, 0.68), (6, 45, 3, 18)] In Python, the fastest way to sort multiple sequences is to sort multiple sequences. No tricks, nothing fancy, just: f.sort() i.sort() Don't use sorted() unless you have to keep the unsorted list as well, because sorted makes a copy of the data. In other words, don't do this: f = sorted(f) # No! Bad! but you can do this: old_f = f f = sorted(f) > but my sequences contain 10,000+ elements and the sort is performed thousands > of times. Is there a faster solution? Ten thousand elements is not very many. Why do you need to sort thousands of times? What are you doing with the data that it needs repeated sorting? Python's sort routine is implemented in C, highly optimized, and is extremely fast. It is especially fast if the data is already almost sorted. So if you have a list of sorted data, and you add one item to the end, and re-sort, that will be *extremely* fast. There is literally nothing you can write in pure Python that will even come close to the speed of Python's sort. Unless you have profiled your application and discovered that sorting is the bottleneck making the app too slow, you are engaged in premature optimization. Don't try and guess what makes your code slow, measure! -- Steven
_______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
