Re: Is there an STL algo to fill a vector with product of 2 other vectors?

From:

James Kanze <james.kanze@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Wed, 10 Dec 2008 01:37:13 -0800 (PST)

Message-ID:

<c8dac7a6-f1e1-4019-9793-72495e24b92b@e6g2000vbe.googlegroups.com>

On Dec 9, 7:54 pm, Steve555 <foursh...@btinternet.com> wrote:

On 9 Dec, 17:09, James Kanze <james.ka...@gmail.com> wrote:

On Dec 9, 3:43 pm, Steve555 <foursh...@btinternet.com> wrote:

I'm looking for an algorithm that takes 2 vectors and a
function pointer as arguments? I want to use the function
pointer to calculate a result e.g. the product, and put
the result either in place, or in a third vector. I've
looked through the list of algorithms and there doesn't
appear to be one. transform() is the closest, but alas
works on only a single vector.

There are two versions of std::transform. The following code
should do the trick:
    assert( v1.size() == v2.size() ) ;
    std::transform( v1.begin(), v1.end(),
                    v2.begin(),
                    std::back_inserter( v3 ),
                    std::multiplies< double >() ) ;

Thanks James, but I wasn't sure why you used
std::back_inserter()?

Just to have an example. In the above code, the results are put
into a third, initially empty array. If you want them to
replace the contents of one of the original arrays, you
v1.begin() or v2.begin() instead. (The advantage of using
back_inserter here is that it makes it clear that this argument
is the output, since a back_insert_iterator can only be used for
output.)

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