Re: std::set as search tree - manipulate elements?
On Jul 17, 1:54 am, Rune Allnor <all...@tele.ntnu.no> wrote:
Hi all.
I would like to use std::set to implement a histogram.
In essence the histogram contains some elements
struct histbin{
int bin;
int count;
/* constructors */
bool operator<(const histbin& h) const {return bin < h.bin;};
};
where histbin::bin denotes the range of each bin and
histbin::count denotes the number of hits.
The problem is how to build the histogram. Since
std::set is specified to have O(log n) search time,
it must necessarily be implemented as some sort of
tree structure. I would like to exploit this to do
something like
std::set<histbin> histogram;
std::set<histbin>::iterator i;
while (/* data coming in */)
{
i=histogram.find(data);
if (i!=histogram.end())
{
(*i).count+=1; // <<<<<======
}
else
{
/* insert new bin */
}
}
The problem is the tagged line. Apparently, all elements
in std::set are declared 'const', so I am not allowed to
manipulate the elements directly. Do note that I do *not*
manipulate the histbin::bin element, which is used as the
key for sorting, and thus it ought to be safe to manipulate
the histbin::count elements.
Is there a convemient, safe way to be able to use std::set
as the search tree for this histogram?
If 'no', are there other STL containesr that can be used?
I would prefer not to have to implement a tree from scratch,
but if there are no alternatives I would like to know that
early on, and just get to work...
Could you instead use a map?
std::map<int,histbin> histogram;
std::map<int,histbin>::iterator finditr;
while (/* data coming in */)
{
finditr=histogram.find(i);
if (finditr!=histogram.end())
{
finditr->second.icount+=1;
}
else
{
/* insert new bin */
}
}
The find function on the map is also Logarithmic. They keys are
internally stored as sorted already and you don't need to worry about
that part.
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