|Problems? Is your data what you think it is?|
Re: map versus forby dHarry (Abbot)
|on Aug 05, 2008 at 07:36 UTC||Need Help??|
Instead of replying to every individual response Iíll write a "one-to-many".
First of all thanks monks for the many reactions. Some of them are really useful and give me insight in the tradeoffs involved en when to prefer one over the other. I especially like the responses of dragonchild, Fletch and pc88mxer which I think are the most useful to me.
I can fully appreciate the obvious advantages that map has over for and there is no doubt that using map is usually the better choice. But my eye was drawn to the following two paragraphs:
"There are a couple of other advantages that arenít quite as obvious. For example, when you use map, most of your looping and list generation is being done in heavily optimized compiled C-code, not in interpreted Perl. So itís usually being done considerably faster.
In addition, the map knows in advance exactly how many elements it will eventually process, so it can pre-allocate sufficient space in the list itís returning. Or rather it can usually pre-allocate sufficient space. If the mapís block returns more than one value for each element of the original list, then extra allocations will still be necessary. But, even then, not as many as the equivalent series of push statements would require."
(taken from PBP p11, paragraphs 4 and 5)
I can understand this in no other way then map is usually faster then for. Apparently the example given by Damian doesnít show the difference. It would be interesting to construct an example which shows the advantage in performance for map over for. So far I have not succeeded in doing this.