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Groups > comp.lang.c++ > #118682

std::map advocacy

From Michael S <already5chosen@yahoo.com>
Newsgroups comp.lang.c++
Subject std::map advocacy
Date 2024-04-07 18:38 +0300
Organization A noiseless patient Spider
Message-ID <20240407183854.00000797@yahoo.com> (permalink)
References (6 earlier) <uupmvv$1j8sq$1@raubtier-asyl.eternal-september.org> <03_PN.124502$U1cc.11575@fx04.iad> <uurm8q$24ka4$1@dont-email.me> <20240407160050.00004370@yahoo.com> <uuu98b$2qou0$1@dont-email.me>

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On Sun, 7 Apr 2024 16:06:02 +0200
David Brown <david.brown@hesbynett.no> wrote:

> 
> Different people have different needs from C++, and use different 
> features.  If I were programming on a PC, I'd happily use std::map<>
> and the like.  But I don't program on PC's, and I don't use
> std::map<>.  If I needed something like that, I'd make my own class
> that fitted my requirements tightly - a factor of 10 inefficiency is
> often fine on big systems, but not on the devices I work with.
> 
> But that's all fine - use whatever you find useful from the language.
> 
> 

Factor of 5-10 (mentioned in my other post) is quite rare and mostly
applies not to std::map vs custom implementation of RB or AVL tree, but
to std::map vs some form of hash, esp. when the nature of the key is
such that relatively simple hash function happens to have good
collision avoidance properties and when the database is huge, so O(1)
vs O(logN) starts to be significant.

Also pay attention that in situations where you do a lot of insertions
and deletions, and especially of deletions followed by insertions,
std::map::extract() could be of great help in reducing a cost of memory
allocation/delallocation to necessary minimum. It's relatively new
addition to std::map (C++17) and I'd guess that many C++ programmers
are not aware of its existence.

In my recent experience (I was implementing median filter over window
of few 1000s values), a use of extract() made clean and simple
std::map-based solution (well, actually std::multiset in this
particular case, but the same principles applies to
std::set/multiset/amp/multymap) faster than relatively more complicated
code based on boost:intrusive:map.

In this case I happened to have enough time to rewrite it in C with
my own implementation of AVL tree. My own code was only some 10 or
15% faster than std container's. And it took more than a day (may be
more than two days? I don't remember) to write and to debug. And that's
for me, who knows the algorithm (from TAoCP) for more than 40 years.
For somebody else it could easily take a weak.
In short, std::map and relatives is quite good piece of work.
Highly recommended. Consider me fan.

At the end in particular case of my unusually long median filter, it
turned out that AVL or RB tree is not the best structure for the job. A
couple of other structures (heap and tournament tree) work better. But
they don't work much better, only by factor of ~2.5. However both heap
and tournament tree are far less generically applicable data structures
than AVL/RB tree. They just happened to be better in this quite
special case.

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Thread

Ain't that beautiful ? Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-04 20:11 +0200
  Re: Ain't that beautiful ? Michael S <already5chosen@yahoo.com> - 2024-04-04 21:55 +0300
    Re: Ain't that beautiful ? Sam <sam@email-scan.com> - 2024-04-04 20:00 -0400
      Re: Ain't that beautiful ? scott@slp53.sl.home (Scott Lurndal) - 2024-04-05 00:21 +0000
        Re: Ain't that beautiful ? Michael S <already5chosen@yahoo.com> - 2024-04-05 17:44 +0300
          Re: Ain't that beautiful ? Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-05 17:27 +0200
            Re: Ain't that beautiful ? Michael S <already5chosen@yahoo.com> - 2024-04-05 18:37 +0300
              Re: Ain't that beautiful ? Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-05 18:04 +0200
                Re: Ain't that beautiful ? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-04-06 15:55 -0700
                Re: Ain't that beautiful ? Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-07 08:28 +0200
                Re: Ain't that beautiful ? scott@slp53.sl.home (Scott Lurndal) - 2024-04-07 15:51 +0000
                Re: Ain't that beautiful ? Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-07 19:35 +0200
                Re: Ain't that beautiful ? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-04-07 12:21 -0700
    Re: Ain't that beautiful ? Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-05 05:05 +0200
      Re: Ain't that beautiful ? Michael S <already5chosen@yahoo.com> - 2024-04-05 17:52 +0300
        Re: Ain't that beautiful ? Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-05 17:26 +0200
          Re: Ain't that beautiful ? scott@slp53.sl.home (Scott Lurndal) - 2024-04-05 20:00 +0000
            Re: Ain't that beautiful ? Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-05 22:29 +0200
              Re: Ain't that beautiful ? scott@slp53.sl.home (Scott Lurndal) - 2024-04-05 21:29 +0000
                Re: Ain't that beautiful ? Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-06 09:06 +0200
                Re: Ain't that beautiful ? Paavo Helde <eesnimi@osa.pri.ee> - 2024-04-06 17:29 +0300
                Re: Ain't that beautiful ? scott@slp53.sl.home (Scott Lurndal) - 2024-04-06 14:56 +0000
                Re: Ain't that beautiful ? Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-06 18:34 +0200
                Re: Ain't that beautiful ? wij <wyniijj5@gmail.com> - 2024-04-07 03:00 +0800
                Re: Ain't that beautiful ? Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-07 08:28 +0200
                Re: Ain't that beautiful ? wij <wyniijj5@gmail.com> - 2024-04-08 07:47 +0800
                Re: Ain't that beautiful ? Michael S <already5chosen@yahoo.com> - 2024-04-07 15:25 +0300
                Re: Ain't that beautiful ? Michael S <already5chosen@yahoo.com> - 2024-04-07 16:00 +0300
                Re: Ain't that beautiful ? David Brown <david.brown@hesbynett.no> - 2024-04-07 16:06 +0200
                Re: Ain't that beautiful ? Michael S <already5chosen@yahoo.com> - 2024-04-07 18:37 +0300
                Re: Ain't that beautiful ? scott@slp53.sl.home (Scott Lurndal) - 2024-04-07 15:58 +0000
                Re: Ain't that beautiful ? David Brown <david.brown@hesbynett.no> - 2024-04-07 18:00 +0200
                Re: Ain't that beautiful ? Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-07 19:38 +0200
                std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-07 18:38 +0300
                Re: std::map advocacy David Brown <david.brown@hesbynett.no> - 2024-04-07 18:06 +0200
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-07 19:35 +0300
                Re: std::map advocacy David Brown <david.brown@hesbynett.no> - 2024-04-08 11:29 +0200
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-08 13:34 +0300
                Re: std::map advocacy wij <wyniijj5@gmail.com> - 2024-04-08 19:18 +0800
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-08 16:32 +0300
                Re: std::map advocacy wij <wyniijj5@gmail.com> - 2024-04-09 08:40 +0800
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-09 12:48 +0300
                Re: std::map advocacy Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-09 13:16 +0200
                Re: std::map advocacy David Brown <david.brown@hesbynett.no> - 2024-04-08 15:30 +0200
                Re: std::map advocacy scott@slp53.sl.home (Scott Lurndal) - 2024-04-08 17:19 +0000
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-09 00:47 +0300
                Re: std::map advocacy scott@slp53.sl.home (Scott Lurndal) - 2024-04-08 23:00 +0000
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-09 02:20 +0300
                Re: std::map advocacy scott@slp53.sl.home (Scott Lurndal) - 2024-04-09 15:22 +0000
                Re: std::map advocacy David Brown <david.brown@hesbynett.no> - 2024-04-09 09:11 +0200
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-09 13:12 +0300
                Re: std::map advocacy David Brown <david.brown@hesbynett.no> - 2024-04-09 15:01 +0200
                Re: std::map advocacy Richard Damon <richard@damon-family.org> - 2024-04-08 07:10 -0400
                Re: std::map advocacy David Brown <david.brown@hesbynett.no> - 2024-04-08 15:45 +0200
                Re: std::map advocacy James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-04-08 19:42 -0400
                Re: std::map advocacy David Brown <david.brown@hesbynett.no> - 2024-04-09 09:45 +0200
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-09 13:27 +0300
                Re: std::map advocacy David Brown <david.brown@hesbynett.no> - 2024-04-09 15:13 +0200
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-09 18:12 +0300
                Re: std::map advocacy David Brown <david.brown@hesbynett.no> - 2024-04-09 18:22 +0200
                Re: std::map advocacy James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-04-10 02:24 -0400
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-11 00:07 +0300
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-11 16:18 +0300
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-11 16:39 +0300
                Re: std::map advocacy Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-11 16:21 +0200
                Re: std::map advocacy Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-11 15:31 +0200
                Re: std::map advocacy wij <wyniijj5@gmail.com> - 2024-04-11 22:40 +0800
                Re: std::map advocacy David Brown <david.brown@hesbynett.no> - 2024-04-11 16:55 +0200
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-11 16:13 +0300
                Re: std::map advocacy Paavo Helde <eesnimi@osa.pri.ee> - 2024-04-11 18:18 +0300
                Re: std::map advocacy David Brown <david.brown@hesbynett.no> - 2024-04-11 09:57 +0200
                Re: std::map advocacy David Brown <david.brown@hesbynett.no> - 2024-04-11 13:47 +0200
                Re: std::map advocacy Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-11 14:04 +0200
                Re: std::map advocacy wij <wyniijj5@gmail.com> - 2024-04-11 19:25 +0800
                Re: std::map advocacy scott@slp53.sl.home (Scott Lurndal) - 2024-04-07 16:09 +0000
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-07 19:48 +0300
                Re: std::map advocacy Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-07 19:45 +0200
                Re: std::map advocacy Paavo Helde <eesnimi@osa.pri.ee> - 2024-04-08 16:37 +0300
                Re: std::map advocacy Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-07 19:44 +0200
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-08 11:15 +0300
                Re: std::map advocacy Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-08 14:09 +0200
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-08 16:26 +0300
                Re: std::map advocacy Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-08 16:54 +0200
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-08 20:52 +0300
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-09 00:17 +0300
                Re: std::map advocacy Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-09 07:34 +0200
                Re: Ain't that beautiful ? Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-07 16:39 +0200
                Re: Ain't that beautiful ? Michael S <already5chosen@yahoo.com> - 2024-04-07 18:41 +0300
                Re: Ain't that beautiful ? Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-07 19:36 +0200
                Re: Ain't that beautiful ? Paavo Helde <eesnimi@osa.pri.ee> - 2024-04-07 18:25 +0300

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