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

From: Deane Yang (deane_yang_at_[hidden])
Date: 2004-03-26 11:57:06

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.

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
>>
>>
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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"