Re: [Boost-users] Comparing two vectors element by element

Subject: Re: [Boost-users] Comparing two vectors element by element
From: Sean Farrow (sean.farrow_at_[hidden])
Date: 2008-09-10 07:48:30

Hi Gevorg:
In this case it's the second, for more background for interest:
Each vector represents a braille cell.
A braille cell has 6 dots hence the std::bitset<6> so:
A vector can have up to 6 bitsets, each bitset represents one dots
state. 
Hth.
Sean.
 

-----Original Message-----
From: boost-users-bounces_at_[hidden]
[mailto:boost-users-bounces_at_[hidden]] On Behalf Of Gevorg
Voskanyan
Sent: 10 September 2008 11:19
To: boost-users_at_[hidden]
Subject: Re: [Boost-users] Comparing two vectors element by element

Sean Farrow wrote:
> Hi:
> The code doesn't compile here as std:bitsetdoesn't define the <
> operator according to visual studio. I have a custom operator defined
as
> a structure:
> struct BitSetComp
> {
>     bool operator()(const std::bitset<6>& lhs, const std::bitset<6>&
> rhs) const
>     {
>         return lhs.to_ulong() < rhs.to_ulong();
>     }
> };
> How can I use this in the code you providee, or do I need to redefine
in
> a certain way?
> Cheers
> Sean.

[snip]

Hi Sean,

The answer depends on how you define one vector being less than another.

E.g. given the following vectors:

typedef std::bitset< 6 > my_bitset;
typedef std::vector< my_bitset > my_bitset_vector;
my_bitset_vector
   v1 = { my_bitset( "1100" ), my_bitset( "1101" ) },
   v2 = { my_bitset( "1110" ), my_bitset( "1000" ) },
   v3 = { my_bitset( "1101" ), my_bitset( "1111" ), my_bitset( "1010" )
},
   v4 = { my_bitset( "1100" ), my_bitset( "1101" ), my_bitset( "1001" };

how shall these vectors compare to each other?

#1. Lexicographical comparison -   v1 < v2 is true, v1 < v3 is true, v2
< v3 is false, v1 < v4 is true, ...

#include <algorithm>

bool bitset_vector_less_1( const my_bitset_vector& lhs, const
my_bitset_vector& rhs )
{
   return std::lexicographical_compare( lhs.begin(), lhs.end(),
rhs.begin(), rhs.end(), BitSetComp() );
}

#2. Each element of the first vector shall be less than the correponding
element of the second vector - v1 < v2 is false, v2 < v1 is false, v4 <
v3 is true,
(here it is not immediately clear how would one compare vectors of
different size such as v1 and v3)

bool bitset_vector_less_2( const my_bitset_vector& lhs, const
my_bitset_vector& rhs )
{
   assert( lhs.size() == rhs.size() );
   return std::equal( lhs.begin(), lhs.end(), rhs.begin(), BitSetComp()
);
}

If you mean something else, explain your requirement with more detail
and I will try to offer some more help.

HTH,

Best Regards,
Gevorg

P.S.
Sorry but the answer is not strictly boost-related

      
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