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Multiple sort?

 
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BCC
Guest
PostPosted: Thu Jul 22, 2004 11:00 pm    Post subject: Multiple sort? Reply with quote


Hi,

I'm looking for some way to do a multiple sort on a vector of objects based
on the contents of the objects. For example if my vector is of these
objects:

class MyClass
{
public:
double value1;
double value2;
double value3;
};

So I would want to sort by each value in combination...

Is there an existing function to do this already somewhere? Do I need to
roll my own? Any suggestions for the fastest algorithm to use for this
(websites or books)?

Thanks,
B


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Mike Wahler
Guest
PostPosted: Fri Jul 23, 2004 1:12 am    Post subject: Re: Multiple sort? Reply with quote



"BCC" <bryan (AT) akanta (DOT) com> wrote

Quote:
Hi,

I'm looking for some way to do a multiple sort on a vector of objects
based
on the contents of the objects. For example if my vector is of these
objects:

class MyClass
{
public:
double value1;
double value2;
double value3;
};

So I would want to sort by each value in combination...

Is there an existing function to do this already somewhere?

There is ('std::sort', declared by <algorithm>), but you need
to help. Define appropriate comparison operators ('operator<()'),
each of which you pass as an argument to 'std::sort'.

Quote:
Do I need to
roll my own?

Only part of it.

Quote:
Any suggestions for the fastest algorithm to use for this

I'd use 'std::sort', and only pursue other options if it
proved insufficient.

Quote:
(websites or books)?

www.josuttis.com/libbook

-Mike



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rossum
Guest
PostPosted: Fri Jul 23, 2004 8:32 pm    Post subject: Re: Multiple sort? Reply with quote


On Thu, 22 Jul 2004 23:00:37 GMT, "BCC" <bryan (AT) akanta (DOT) com> wrote:

Quote:
Hi,

I'm looking for some way to do a multiple sort on a vector of objects based
on the contents of the objects. For example if my vector is of these
objects:

class MyClass
{
public:
double value1;
double value2;
double value3;
};

So I would want to sort by each value in combination...

Is there an existing function to do this already somewhere? Do I need to
roll my own? Any suggestions for the fastest algorithm to use for this
(websites or books)?

Thanks,
B

#include <algorithm

#include #include <cstdlib>

class MyClass
{
public:
double value1;
double value2;
double value3;

// Friends not necessary with public data,
// required with private data.
friend bool less1(const MyClass& a, const MyClass& b);
friend bool less2(const MyClass& a, const MyClass& b);
friend bool less3(const MyClass& a, const MyClass& b);
friend bool less_sum(const MyClass& a, const MyClass& b);
};

inline bool less1(const MyClass& a, const MyClass& b)
{ return a.value1 < b.value1; }

inline bool less2(const MyClass& a, const MyClass& b)
{ return a.value2 < b.value2; }

inline bool less3(const MyClass& a, const MyClass& b)
{ return a.value3 < b.value3; }

inline bool lessSum(const MyClass& a, const MyClass& b)
{ return (a.value1 + a.value2 + a.value3) < (b.value1 +
b.value2 + b.value3); }


main() {
std::vector
// Sort by value1
std::sort(mcVec.begin(), mcVec.end(), less1);

// Sort by value2
std::sort(mcVec.begin(), mcVec.end(), less2);

// Sort by value3
std::sort(mcVec.begin(), mcVec.end(), less3);

// Sort by sum of all three values
std::sort(mcVec.begin(), mcVec.end(), lessSum);

return EXIT_SUCCESS;
} // end main()



--

The ultimate truth is that there is no Ultimate Truth

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