Dear Sir,

I'm terribly sorry if my description was not clear. You are right about my statement above, it was not precise, the first one it should be:

If the index difference of two consecutive elements of the array is 1 take the 1st colum of all the array i.e  $sample->[0] .. $sample->[-1] PLUS the 2nd column of the last element of the array   $sample->[-1].

Let me give you the illustration of how I get the result. Basically those enclosed with bar (|) and dash (_) are the one which get selected. Notice also the index difference change.

my $sample1     |str1 |index = 1
                |str3 |index = 2
                |str5 |index = 3
                |str7 |index = 4
                |     |_______________
                |str9 str10 index = 5
                |______________________

my $sample2     |str1 str2 | index = 0
                |_________ |
                |str3 str4 | index = 4'
                |__________|

my $sample3      |str1 |   index = 3
                 |     |_________
                 |str3 str4 index = 4
                 ____________________


my $sample4 =   |str1 | index = 1
                |str3 | index = 2
                |str5 | index = 3
                |     |______________
                |str7 str8  index = 4
                ____________________

                
                |str7 str8 | index = 4
                |__________|
                |str9 str10| index = 6
                ___________
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I hope it's clear to you now