Re: transform
"Chris Roth" <czr137@mail.usask.ca> wrote in message
news:ers6av$ujp$1@webmail.usask.ca...
I'm just starting out using the algorithms in c++ std library.
I have a vector of vectors (v) and want to get a slice at some index.
ex. If v held two vectors, v1 and v2:
v1 = 1 2 3 4 5 6
v2 = 7 7 8 8 9 9
the slice at position 3 would be 3 8 (v1(3) and v2(3)).
I think it is possible to use transform to make the slice matrix, but I'm
having trouble with the final argument:
vector< vector<double> > v;
// populate v
vector<double> slice;
transform( v.begin(), v.end(), slice.begin(), ??? );
What goes in ???
I have tried std::vector<double>::at(), but it didn't work.
Thanks c++ board.
You would actually need for_each with your own predicate and not transform.
However, IMHO using one of the generic algorithms supplied by the standard
library is a little overblown in that case. The slice you are referring to
is simply one columen of the matrix. So why not loop over all rows and
extract the value at the position you're looking for.
Something along the lines of the following (untested code!) should do the
trick:
for( vector<vector<double> >::iterator Iter = Matrix.begin(); Iter !=
Matrix.end(); ++Iter ) {
Slice.push_back( Iter->at(ColIndex) );
}
Cheers
Chris