On 3 November 2013 22:55, Jeff Flinn <Jeffrey.Flinn@gmail.com> wrote:
On 11/1/2013 7:24 PM, Travis Gockel wrote:
On Fri, Nov 1, 2013 at 1:18 PM, Jeff Flinn <Jeffrey.Flinn@gmail.com<mailto:Jeffrey.Flinn@gmail.com>> wrote:<mailto:Jeffrey.Flinn@gmail.__com
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>using boost::range::adaptors::__filtered like:
<mailto: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>>
<mailto: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 viewhttp://www.boost.org/doc/libs/__1_55_0b1/libs/icl/doc/html/__boost_icl/projects.html#boost___icl.projects.large_bitset
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>
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.
I would recommend checking out Google sparsehash -- specifically,
sparse_hash_set<T>:
http://code.google.com/p/sparsehash/source/browse/trunk/src/sparsehash/sparse_hash_set
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).
That's 2x10^6 bits for the OP's case, where-as the ICL approach is 64bits per interval. In the OP's case that would be 64x100(max number of invalid items assuming all invalid separated by atleast 1 valid item) about 3 orders of magnitude less.
JeffThanks for the various answers. I'm reading about ICL, and sparsehash to learn more.basically,struct MyPOD { double d1; ..... double d8; }and I currently have std::vector<MyPOD> with 1e6 elements.100 of those would be == a particular instance of MyPOD invalid { +Inf, +Inf, ... -Inf,, 0. }. It's a known, predefined MyPOD constantI need:1. calculate the max element, and the min element, _while_ ignoring the 100 or so invalid entries (I don't know where they are), I can't however change the vector<MyPOD>. it's read only.2. I need also to plot it (ie, plot all the elements that are not Invalid).The index of each element in vector is transformed and returns a sort of coordinate to plot a point
So, I would have wrapped this vector into a class, and exposed similar interface to vector, but would have implemented an iterator that just skips the invallid entries:the iterator would skip the invalid entry until next valid one when incremented or decremented.My class would also be indexable with [] with this access not with the same order as vector's [] (it would skip the invalid entries, so slower)Perhaps the best choice is a boost range adapted view.Reading the docs....thanks very muchMM