Prev: how to non-default construct with multiple virtual inheritance??
Next: Access method names for std::random
From: ManicQin on 2 Jun 2010 05:06
Hi,

I hope the subject wasn't too obfuscated,
Let's say that I have a vector<string> and a function

size_t foo(string inVal)
{
return someNumberRelatedToTheString;
}

I want to accumulate the return values of foo calls.

currently I failed doing it in a one accumulate call so I broke it
into
transform call that inserts the returns to a vector and than
accumulate the vector

Is there a way to do it in one accumulate call?

thanks.

--
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]

From: Paul Bibbings on 2 Jun 2010 17:29
On Jun 2, 9:06 pm, ManicQin <manic...(a)gmail.com> wrote:
> Hi,
>
> I hope the subject wasn't too obfuscated,
> Let's say that I have a vector<string> and a function
>
> size_t foo(string inVal)
> {
> return someNumberRelatedToTheString;
>
> }
>
> I want to accumulate the return values of foo calls.
>
> currently I failed doing it in a one accumulate call so I broke it
> into transform call that inserts the returns to a vector and than
> accumulate the vector
>
> Is there a way to do it in one accumulate call?

You may be able to adapt something along the following lines to suit
your requirements.

#include <string>
#include <vector>
#include <numeric>
#include <functional>
#include <cstddef>
#include <iostream>

size_t foo(std::string inVal)
{
return inVal.size();
}

struct counter
: public std::binary_function<size_t, std::string, size_t>
{
typedef std::binary_function<
size_t,
std::string,
size_t
> bin_func;
typedef bin_func::first_argument_type first_argument_type;
typedef bin_func::second_argument_type second_argument_type;
typedef bin_func::result_type result_type;
result_type operator()(first_argument_type Arg1,
second_argument_type Arg2)
{
return Arg1 + foo(Arg2);
}
};

int main()
{
std::vector<std::string> string_vec;
string_vec.push_back("one");
string_vec.push_back("two");
string_vec.push_back("three");

size_t count = std::accumulate(string_vec.begin(),
string_vec.end(),
0,
counter());
std::cout << "count: " << count << '\n';
}

/**
* Output:
* count: 11
*/

Regards

Paul Bibbings


--
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]

From: AnonMail2005 on 2 Jun 2010 17:29
On Jun 2, 4:06 pm, ManicQin <manic...(a)gmail.com> wrote:
> Hi,
>
> I hope the subject wasn't too obfuscated,
> Let's say that I have a vector<string> and a function
>
> size_t foo(string inVal)
> {
> return someNumberRelatedToTheString;
>
> }
>
> I want to accumulate the return values of foo calls.
>
> currently I failed doing it in a one accumulate call so I broke it
> into
> transform call that inserts the returns to a vector and than
> accumulate the vector
>
> Is there a way to do it in one accumulate call?

There may be but writing your own functor is very straight forward.

// accumulate functor. make it a class (with private members) if you
wish
struct MyFunctor
{
MyFunctor(size_t & total) : m_total(total)
{}

void operator () (const std::string & s) const
{
m_total += s.size();
}

// reference to external variable
size_t & m_total;
};

Sample usage where v is your vector of strings:
size_t total = 0;
std::for_each(v.begin(), v.end(), MyFunctor(total));

HTH


--
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]

From: mingze zhang on 2 Jun 2010 17:32
On Jun 3, 4:06 am, ManicQin <manic...(a)gmail.com> wrote:
> Hi,
>
> I hope the subject wasn't too obfuscated,
> Let's say that I have a vector<string> and a function
>
> size_t foo(string inVal)
> {
> return someNumberRelatedToTheString;
>
> }
>
> I want to accumulate the return values of foo calls.
>
> currently I failed doing it in a one accumulate call so I broke it
> into
> transform call that inserts the returns to a vector and than
> accumulate the vector
>
> Is there a way to do it in one accumulate call?
>
> thanks.

{ quoted banner removed; please do it yourself. -mod }

use for_each

vector<string> a;
a.push_back("abc");
a.push_back("def");
int b = 0;
for_each(a.begin(), a.end(), [&b](const string &inVal){ b = b +
foo(inVal); });


--
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]

 | 
Pages: 1
Prev: how to non-default construct with multiple virtual inheritance??
Next: Access method names for std::random