Re: [Boost-users] Re: Defining less on member variables/functions

From: Victor A. Wagner Jr. (vawjr_at_[hidden])
Date: 2004-03-26 14:25:01

At Friday 2004-03-26 09:57, you wrote:
>I can't speak for the original poster, but I often have
>a collection of pairs of the form (time, data) and want
>to put the whole thing in chronological order.

if .first is unique (which it would be in your case) letting the standard 
operator< for std::pair<> suffices (unless one is extremely hyper about how 
"fast" things go).

>Victor A. Wagner Jr. wrote:
>>why do you want to sort ONLY on the 1st element of the pair?
>>At Thursday 2004-03-25 11:34, you wrote:
>>
>>>content-class: urn:content-classes:message
>>>Content-Type: multipart/alternative;
>>>         boundary="----_=_NextPart_001_01C41297.D800D40A"
>>>
>>>I've had this same pattern come up 4 or 5 times now, and each time I've 
>>>been unable to find a stl + boost solution that allowed me to do what I 
>>>want without writing my own less function.  Basically, I want something 
>>>that will let me do a sort, or define a map on structs or pairs without 
>>>writing a less that compares the member variable or ..first.  My last attempt:
>>>
>>>vector<pair<float, float>> myVector
>>>std::sort(myVector.begin(), myVector.end(), _1.first < _2.first);
>>>
>>>No such luck.  It looks like I can do operator * and & on lambda 
>>>objects, but not access members through them.  Is there anything in 
>>>boost, stl, or elsewhere that lets me not write this:
>>>
>>>class myLess
>>>{
>>>     bool operator() (pair<float, float> a, pair<float, float>b)
>>>         {return a.first < b.first;}
>>>}
>>>
>>>Thanks for any help,
>>>Chris
>>>
>>>
>>>_______________________________________________
>>>Boost-users mailing list
>>>Boost-users_at_[hidden]
>>>http://lists.boost.org/mailman/listinfo.cgi/boost-users
>>
>>Victor A. Wagner Jr.      http://rudbek.com
>>The five most dangerous words in the English language:
>>               "There oughta be a law"
>
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Victor A. Wagner Jr.      http://rudbek.com
The five most dangerous words in the English language:
               "There oughta be a law"