index of std::vector with condition

From:

Philipp Kraus <philipp.kraus@flashpixx.de>

Newsgroups:

comp.lang.c++

Date:

Mon, 12 Jul 2010 23:50:13 +0200

Message-ID:

<i1g2ml$7ic$1@online.de>

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Hello,

is there a fast way to create a index with condition of a std::vector?
For illustrating:

I have a vector mydata with some data and I would like to create a
vector with unique elements

std::vector<T> l_unique( mydata );
std::sort( l_unique.begin(), l_unique.end() );
l_unique.erase( std::unique( l_unique.begin(), l_unique.end()),
l_unique.end() );

in the next step I will do this

std::vector< std::vector<std::size:t> > index;
for(std::size_t i=0; i < l_unique.size(); ++i) {
 std::vector<std::size_t> y;

 for(std::size_t n=0; n < mydata.size(); ++n)
 if (mydata[n] == l_unique[i])
 y.push_back(n);

 index.push_back(y);
}

Can I do this two for loops more efficient? I would like to get the
index position in my data vector from a unique set of the elements
within the vector.

Thanks for help

Phil
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Hello,
 
is there a fast way to create a index with condition of a std::vector?
For illustrating:
 
I have a vector mydata with some data and I would like to create a vector with unique elements
 
std::vector<T> l_unique( mydata );
std::sort( l_unique.begin(), l_unique.end() );
l_unique.erase(? std::unique( l_unique.begin(), l_unique.end()), l_unique.end()? );
 
in the next step I will do this
 
std::vector< std::vector<std::size:t> > index;
for(std::size_t i=0; i < l_unique.size(); ++i) {
? ? ? std::vector<std::size_t> y;
?? ? ?
? ? ? for(std::size_t n=0; n < mydata.size(); ++n)
 if (mydata[n] == l_unique[i])
 y.push_back(n);
 
 index.push_back(y);
}
 
Can I do this two for loops more efficient? I would like to get the index position in my data vector from a unique set of the elements within the vector.
 
Thanks for help
 
Phil
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