From: Rusi <rustompmody@gmail.com>
To: help-gnu-emacs@gnu.org
Subject: Re: return first element in list with certain property
Date: Wed, 22 Nov 2017 06:52:20 -0800 (PST) [thread overview]
Message-ID: <e1e3532f-b59f-42ff-819d-ff81de697c96@googlegroups.com> (raw)
In-Reply-To: <20171121225216.17011915608ecbb6021c9bc2@speakeasy.net>
On Wednesday, November 22, 2017 at 9:22:18 AM UTC+5:30, James K. Lowden wrote:
> On Tue, 21 Nov 2017 19:37:01 +0100
> Michael Heerdegen wrote:
>
> > Philipp Stephani writes:
> >
> > > Please consider Knuth's statement about premature optimization.
> > > Until your users have actually complained about the speed of your
> > > product and you have benchmarked it and isolated cl-find-if as the
> > > culprit, there's no need to micro-optimize. Presumably cl-find-if
> > > has performed two iterations for years or decades without anybody
> > > being bothered enough to improve it.
> >
> > Not only that. Seems the second iteration is at least ~50 times
> > faster than the first one (using `elt' that is much faster than a
> > loop), so it doesn't matter anyway. If your program is slow, the
> > second iteration will never be the culprit.
>
> Not only that. ;-) Traversing the list twice is still O(n).
>
> I would guess in elisp the typical list is on the order of a dozen
> elements. As Rob Pike says,"Fancy algorithms are slow for small N, and
> N is almost always small."
>
> No matter how long the list is, it traversing it twice will only take
> at most twice as long. If your design fails when your data size
> doubles, you have problems emacs won't solve.
I dont think its quite as simple as that…
Consider python wherein
- C is typically 2 orders of magnitude (hundreds of times) faster than python
- the two can cohabit quite closely; eg moving a ordinary python loop to a
vector numpy operation implicitly moves python to C with corresponding speedup
(and speed-down due to conversion etc)
And so the two versions are not just comparing loop vs loop-loop
but loop₁ vs loop₂ - loop₃
where the ₁₂₃ can vary across {interpreter, bare-metal}
we could have all manner of possibilities of speedup and speed-down
Sure its not nearly as simple to add C to elisp as to python
However it is essentially the same thing: elisp and python are interpreters
sitting on top of C. Which in big-O terms means 1 loop vs 2 constant multiplier
vs bare-metal vs interpretive overhead multiplier
next prev parent reply other threads:[~2017-11-22 14:52 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-19 20:43 return first element in list with certain property Emanuel Berg
2017-11-19 20:51 ` Eric Abrahamsen
2017-11-19 21:37 ` Philipp Stephani
2017-11-19 22:55 ` Emanuel Berg
2017-11-20 18:51 ` John Mastro
2017-11-20 19:21 ` Michael Heerdegen
2017-11-20 21:20 ` Emanuel Berg
2017-11-20 21:40 ` John Mastro
2017-11-20 22:19 ` Michael Heerdegen
2017-11-20 20:52 ` Emanuel Berg
2017-11-20 20:12 ` Drew Adams
2017-11-20 20:49 ` Eric Abrahamsen
2017-11-20 21:16 ` Emanuel Berg
2017-11-20 22:02 ` Eric Abrahamsen
2017-11-21 1:54 ` Emanuel Berg
2017-11-21 2:18 ` Emanuel Berg
2017-11-21 17:34 ` Michael Heerdegen
2017-11-21 20:10 ` Emanuel Berg
2017-11-21 21:33 ` Michael Heerdegen
2017-11-22 21:30 ` Nicolas Petton
2017-11-22 21:31 ` Nicolas Petton
2017-11-21 18:01 ` Philipp Stephani
2017-11-21 18:37 ` Michael Heerdegen
2017-11-21 19:26 ` Drew Adams
2017-11-21 20:17 ` Emanuel Berg
2017-11-21 20:47 ` Drew Adams
2017-11-21 20:14 ` Emanuel Berg
[not found] ` <mailman.4260.1511289435.27995.help-gnu-emacs@gnu.org>
2017-11-22 3:52 ` James K. Lowden
2017-11-22 5:04 ` Michael Heerdegen
2017-11-22 14:06 ` Emanuel Berg
2017-11-22 14:52 ` Rusi [this message]
2017-11-22 21:28 ` Nicolas Petton
2017-11-23 0:56 ` Emanuel Berg
2017-11-23 1:17 ` Michael Heerdegen
2017-11-23 1:30 ` Emanuel Berg
2017-11-25 2:57 ` John Mastro
2017-11-25 3:54 ` Robert Thorpe
2017-11-25 4:44 ` Alexis
2017-11-25 7:10 ` tomas
2017-11-25 17:11 ` Emanuel Berg
2017-11-25 7:46 ` Eli Zaretskii
2017-11-25 8:03 ` tomas
2017-11-25 19:00 ` John Mastro
2017-11-25 19:45 ` Emanuel Berg
2017-11-27 3:44 ` Michael Heerdegen
2017-11-20 22:59 ` Drew Adams
2017-11-21 1:50 ` Emanuel Berg
[not found] ` <mailman.4093.1511127491.27995.help-gnu-emacs@gnu.org>
2018-03-06 0:31 ` Robert L.
2018-03-06 8:53 ` Emanuel Berg
2018-03-06 9:29 ` Emanuel Berg
[not found] <mailman.4086.1511124258.27995.help-gnu-emacs@gnu.org>
2017-11-19 21:19 ` Marco Wahl
2017-11-19 22:51 ` Emanuel Berg
2017-11-21 4:00 ` Emanuel Berg
2017-11-19 21:20 ` Marco Wahl
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