foreach and arrays

mndoci has asked for the wisdom of the Perl Monks concerning the following question:

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Re: foreach and arrays by jwest (Friar) on Apr 19, 2001 at 01:55 UTC
foreach() itterates from one element to the successive element. In order for there to be a successor, there must be a semblance of order, so it's sequentially. Further, foreach() is a synonym for for(), and for `for $index (0 .. $somenumber) { ... };` [download] to work as you expect, it has to be sequential. At least, that's to my understanding. :) Hope this helps! --jwest -><- -><- -><- -><- -><- All things are Perfect To every last Flaw And bound in accord With Eris's Law - HBT; The Book of Advice, 1:7	[reply] [d/l]
Re: foreach and arrays by Sherlock (Deacon) on Apr 19, 2001 at 02:02 UTC
To answer this, execute this block of code to see what happens: `@myArray = (0,0,0,0,0); $myCounter = 1; foreach $item (@myArray) { $item = $myCounter; $myCounter++; } for ( $i = 0; $i < 5; $i++ ) { print "$myArray[$i],"; }` [download] You should get the output "1,2,3,4,5,". This would indicate that the foreach operator work sequentially, as one would expect. -Sherlock	[reply] [d/l]
(jeffa) Re: Re: foreach and arrays by jeffa (Bishop) on Apr 19, 2001 at 03:28 UTC
Just a pointer, in the time it takes you to type `@myArray` or `$myCounter`, you could just as easily type `my @array` or `my $counter` You do enjoy the benifits of lexically binded variables, don't you? Also, you can save some typing with: `my @array = qw(0 0 0 0 0); # well, not much on this one, but . . . my @array = (0)x5; # pure evil` [download] and use Perl for loops like Perl, not like C! `for (0..$#array) { print $array[$_],','; }` [download] jeff R-R-R--R-R-R--R-R-R--R-R-R--R-R-R-- L-L--L-L--L-L--L-L--L-L--L-L--L-L--	[reply] [d/l] [select]
Re: foreach and arrays by Maclir (Curate) on Apr 19, 2001 at 02:20 UTC
My understanding is that a `foreach` loop processes the array sequentially, just as a "standard" `for` loop would do. I think where the statement <quote>there is no way of knowing where in a list one is</quote> comes from is that there is no explicit loop variable - if you want to know where you are up to in the array, you have to keep track of that yourself. However, the `foreach` is generally processing a list, no necessarily an array. I could define the contents of the list explicitly, such as: `print 'I like'; foreach ('spam', 'spam', 'spam', 'eggs', 'and', 'spam') { print " $_"; } print ".\n";` [download] and there is no way of knowing that, for example, when I am printing the work "eggs" that this is the fourth time through the loop. The result is, of course: $ spam.pl I like spam spam spam eggs and spam. $ [download]	[reply] [d/l] [select]
Re: foreach and arrays by Xxaxx (Monk) on Apr 19, 2001 at 05:46 UTC
My guess is that you are dredging up a half remembered comment about a 'foreach' when applied to a hash. `foreach my $key (keys %hashname) { ..... }` [download] In most texts on Perl you will see some reference to the fact that keys will return the keys to the hash but "not in any definite order." I think this is what you were half remembering. Claude	[reply] [d/l]
Re: foreach and arrays by rchiav (Deacon) on Apr 19, 2001 at 02:07 UTC
Just because you don't know where you are in the array, doesn't mean that it isn't processed sequentially. I don't know for a fact that it is, but here's my logic. suppose you do a `foreach $element (@somearray)`. You're then working with `$element` which refrences something in `@somearray`. Now there's no way to tell what `$element` is refrencing in `@somearray` but that doesn't mean that the processing isn't sequential. Rich	[reply] [d/l] [select]