For a beginner, I would not recommend fiddling around with map expressions until the fundamentals of Perl style foreach and while loops are mastered. In my Perl coding, C style for loops are very rare because array indices are relatively rare - Actually even in my C code indices are rare because of the ubiquitous "*pointer++" to access sequential elements of an array.
The OP's problem wasn't related to writing or using a "map" expression, and I said basically that "a map expression is the not the problem or the solution". This appeared to be an algorithm question. Express the algorithm as a for (foreach) loop. Worry about map statements later.
I was taught never to use a map in void context due a big performance penalty. I hear that this performance penalty is much less now. But I still would not use map in a void context because that obscures the intent of the code. I use map for simple transformations (like the code I show below).
I have seen Tom Christiansen write some map's with maybe 15 or so lines of code inside the map. This can be quite elegant in the right situation, but few mortals such as myself encounter such situations. If a map isn't "short", I use a for loop, perhaps even creating some intermediate arrays in the process.
I guess if we get into strange things, consider the following code. It is possible to modify the loop variable within a for loop because Perl sets that up as an alias to the input list. I personally never do this in my code, preferring to create a separate output array. Not everything that is possible should be done.
This is an example where I would, from a style viewpoint use the map expression vs a for loop. @array = map{$_+5}@array; makes it clear that I have modified @array. This is not clear from the for loop. I guess that would be like "using a for loop in a void context?".
The permutations on this are endless. I hope this explains my coding philosophy adequately.
In this case, I am not going to go into some deep dive into deparse to decide whether or not the foreach loop has more efficient code. I would use the map expression because the source code is more clear.use strict; use warnings; my @array = (1,2,3,4,5); foreach my $num (@array) { $num += 5; # completely legal # but obscure } print "@array\n"; #6 7 8 9 10 @array = (1,2,3,4,5); @array = map{$_+5}@array; print "@array\n"; #6 7 8 9 10
In reply to Re^5: How do I use the map command for this?
by Marshall
in thread How do I use the map command for this?
by Anonymous Monk
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