in reply to Re^2: Efficient array element deletion
in thread Efficient array element deletion

for ( reverse 0 .. $#array ) flattens the list.for ( -@array .. -1 ) is better.

Except I don't think that will work either.

J:\> perl -le "@arr = ( 1 .. 10 ); print $arr[ $_ ] for -@arr .. -1;"
1
2
3
4
5
6
7
8
9
10

J:\>

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From the documentation (Range Operators, my emphasis): In list context, it returns a list of values counting (up by ones) from the left value to the right value so I don't think it can be persauded to decrement. So doing

J:\> perl -le "@arr = ( 1 .. 10 ); print $arr[ $_ ] for -1 .. -@arr;"

J:\>

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results in nothing useful.

Cheers,

JohnGG

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Re^4: Efficient array element deletion
by ikegami (Patriarch) on Dec 05, 2008 at 13:07 UTC

    I thought you were referring to the off-by-one error, and didn't notice it also iterated backwards.

    Solutions:
    for ( -$#array..0 ) { ... $array[-$_] ... }
    for ( my $i=@array; $i--; ) { ... $array[$i] ... }

[reply]
[d/l]
[select]

      Here's another approach to accessing the elements of an array in reverse order without creating a list: 

       @a = 1 .. 9;;

print "$_ : -$_ :  $a[ -$_ ]" for 1 .. @a;;
1 : -1 :  9
2 : -2 :  8
3 : -3 :  7
4 : -4 :  6
5 : -5 :  5
6 : -6 :  4
7 : -7 :  3
8 : -8 :  2
9 : -9 :  1

      [download]
      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]
[d/l]
        This is actually what I meant to do originally, I just didn't quite understand how negative indices were interpreted.
[reply]

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