On Fri, Nov 1, 2013 at 1:18 PM, Jeff Flinn <Jeffrey.Flinn@gmail.com> wrote:
On 11/1/2013 1:28 PM, MM wrote:
On 1 November 2013 12:37, Jeff Flinn <Jeffrey.Flinn@gmail.com <mailto:Jeffrey.Flinn@gmail.**com <Jeffrey.Flinn@gmail.com>>> wrote: On 10/31/2013 1:14 PM, MM wrote: On 31 October 2013 16:10, Klaim - Joël Lamotte <mjklaim@gmail.com <mailto:mjklaim@gmail.com> <mailto:mjklaim@gmail.com <mailto:mjklaim@gmail.com>>> wrote:
What would "valid"/"invalid" means here? If it's "exist" or "don't exist", then maybe using boost::optional<MyPod> would be enough.
That's right. How about sizeof( boost::optional<MyPod> ) vs sizeof( MyPOD ) ? Also, what sort of iterator can iterate over just the valid values? or how to implement one? The point here is that there's a small number of elements that are invalid, their indices in the container are random,
So why not keep the invalid items from getting into the container in the first place?
Jeff
because they are processed at a later stage, their indices in the container are relevant,
I'd need a better description of just what defines and item to be valid/invalid. And just what this processed at a later stage means.
If you've some functions:
bool valid(const MyPod& ) { return ...; } bool invalid(const MyPod& pod) { return !valid(pod); }
, and a pre-existing container then you can get an adapted view using boost::range::adaptors::**filtered like:
typedef std::vector<MyPod> MyPods;
MyPods all(...); MyPods bad;
boost::copy(all | filtered(invalid), std::back_inserter(bad));
boost::foreach(all | filtered(valid), someFunction);
It all depends on the context of where this is used. Another approach uses the boost icl (interval container library). One example is:
http://www.boost.org/doc/libs/**1_55_0b1/libs/icl/doc/html/** boost_icl/projects.html#boost_**icl.projects.large_bitset<http://www.boost.org/doc/libs/1_55_0b1/libs/icl/doc/html/boost_icl/projects.html#boost_icl.projects.large_bitset>
I've used a similar approach to just store the "valid" bases in a dna sequences and keeping track of gaps with an interval container. The advantage is avoiding the filtering cost when the application is primarily interested in the valid items only.
Jeff
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I would recommend checking out Google sparsehash -- specifically, sparse_hash_set<T>: http://code.google.com/p/sparsehash/source/browse/trunk/src/sparsehash/spars... The biggest difference between that and something like an std::vector<boost::optional<T>> is google::sparse_hash_set will re-order values on you (the nature of hash tables). It also forces you to have a "deleted key" which exists in the realm of possible T values. Based on impression that I get from your original email, this fits with your idea of an "invalid" T. That said, it is a ridiculously low-overhead container (on the order of ~2 bits/entry vs 4 bytes/entry with a boost::optional). -- Travis Gockel Chief λ Combinator