#                col1 col2  index  
                       
my $sample1 =  ['str1 str2  1',
                'str3 str4  2',
                'str5 str6  3',
                'str7 str8  4',
                'str9 str10 5'];

my $sample2  = ['str1 str2 0',
                'str3 str4 4'];

my $sample3  = ['str1 str2 3',
                'str3 str4 4'];