Re: How to iterate thru entire array with start point other than beginning

[GrandFather]

Slices are fun:

use strict;
use warnings;

my @month_name = qw(
    January February March April May June July August September
    October November December
    );
    
for my $startMonthIdx (0 .. 11) {
    my @sel = @month_name[$startMonthIdx .. 11, 0 .. $startMonthIdx - 
+1];

    print "$startMonthIdx: @sel\n";
}

Prints:

0: January February March April May June July August September October
+ November December
1: February March April May June July August September October Novembe
+r December January
2: March April May June July August September October November Decembe
+r January February
3: April May June July August September October November December Janu
+ary February March
4: May June July August September October November December January Fe
+bruary March April
5: June July August September October November December January Februa
+ry March April May
6: July August September October November December January February Ma
+rch April May June
7: August September October November December January February March A
+pril May June July
8: September October November December January February March April Ma
+y June July August
9: October November December January February March April May June Jul
+y August September
10: November December January February March April May June July Augus
+t September October
11: December January February March April May June July August Septemb
+er October November

[soonix]

no need to concatenate two ranges. Instead of

    my @sel = @month_name[$startMonthIdx .. 11, 0 .. $startMonthIdx - 
+1];

you can use

    my @sel = @month_name[$startMonthIdx - 12 .. $startMonthIdx - 1];

gives the same output as above.

[AnomalousMonk]

The only objection I would make to the array slice approaches of GrandFather here or soonix here (++ to both by the way) is that they start to produce strange results for  $startMonthIdx values outside the  0 .. @month_name range. This may not be a real problem since one may never endeavor to venture outside this range.

The attraction for me of the modulo-@month_name approach is that it gives sensible results for any weird positive or negative range whatever. I would prefer to impose any range limits in a separate step and then just reliably handle whatever range emerged from the validation process.

c:\@Work\Perl\monks>perl -wMstrict -le
"my @months = qw(Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec);
 ;;
 for my $offset (-25 .. -11) {
   printf 'offset %3d: ', $offset;
   my @sel = map $months[ ($_ + $offset) % @months ], -109 .. -95;
   printf qq{@sel};
   print '';
   }
"
offset -25: Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ja
+n
offset -24: Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Fe
+b
offset -23: Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Ma
+r
offset -22: Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Ap
+r
offset -21: Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr Ma
+y
offset -20: Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Ju
+n
offset -19: May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Ju
+l
offset -18: Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Au
+g
offset -17: Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Se
+p
offset -16: Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oc
+t
offset -15: Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct No
+v
offset -14: Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov De
+c
offset -13: Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ja
+n
offset -12: Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Fe
+b
offset -11: Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Ma
+r