Gunnar Hjalmarsson wrote:
Richard Lee wrote:
" It should include '1 2 3' because '1 2 3', '1 2 4', '1 2 7', '1 2 8',
'1 2 9' = '1 2'(the common number from the list) + anynumber. "
as any of them contains 1 and 2 and I don't understand why '1 2 3' was
picked.
My interpretation: Because it's the first element of those with 1 and
2 in them. In other words, the order in which the elements appear in
@datas is important for the result.
Also can someone explain to me in detail what Gunnar Hjalmarsson's
solution is doing?
------------ code of Gunnar's ----------------
my $numbers_wanted = 2;
my ( @datawanted, @numbers );
LOOP: foreach ( @datas ) {
my @test = split;
foreach my $num ( @numbers ) {
next LOOP if grep( $num->{$_}, @test ) >= $numbers_wanted;
}
push @datawanted, $_;
push @numbers, { map { $_ => 1 } @test };
}
print "$_\n" for @datawanted;
It iterates over @datas and stores some of the elements in @datawanted
based on (my interpretation of) the OP's criteria. There is nothing
mysterious with the code; everything can be looked up in the Perl docs.
@numbers is a help variable where the numbers in previously stored
elements are made conveniently accessible for lookups. The expression
map { $_ => 1 } @test
creates a key/value list where the elements of @test are the keys (see
"perldoc -f map"), and
push @numbers, { map { $_ => 1 } @test };
makes the list an anonymous hash and adds a reference to that hash to
@numbers.
grep() is used in scalar context to compare the elements with
previously stored elements and test against the OP's criteria.
perldoc -f grep
why does program go over empty array at the begining?
foreach my $num ( @numbers ) {
next LOOP if grep( $num->{$_}, @test ) >= $numbers_wanted;
}
perl -d ./iii
Loading DB routines from perl5db.pl version 1.25
Editor support available.
Enter h or `h h' for help, or `man perldebug' for more help.
main::(./iii:9): my @datas = (
main::(./iii:10): '1 2 3', '1 2 4', '1 2 7', '1 2 8', '1 2
9', '1 6 7',
main::(./iii:11): '1 7 12', '2 6 7', '4 5 10', '4 5 15'
main::(./iii:12): );
DB<1> s
main::(./iii:14): my $numbers_wanted = 2;
DB<1> x @datas
0 '1 2 3'
1 '1 2 4'
2 '1 2 7'
3 '1 2 8'
4 '1 2 9'
5 '1 6 7'
6 '1 7 12'
7 '2 6 7'
8 '4 5 10'
9 '4 5 15'
DB<2> s
main::(./iii:15): my ( @datawanted, @numbers );
DB<2>
main::(./iii:17): LOOP: foreach ( @datas ) {
DB<2> x $_
0 undef
DB<3> s
main::(./iii:18): my @test = split;
DB<3> x $x-^H^H
Unrecognized character \x08 at (eval
8)[/usr/perl5/5.8.4/lib/perl5db.pl:619] line 2.
eval '($@, $!, $^E, $,, $/, $\\, $^W) = @saved;package main; $^D
= $^D | $DB::db_stop;
$;-
;' called at /usr/perl5/5.8.4/lib/perl5db.pl line 619
DB::eval called at /usr/perl5/5.8.4/lib/perl5db.pl line 3349
DB::DB called at ./iii line 18
DB<4> x $_
0 '1 2 3'
DB<5> x @test
empty array
DB<6> s
main::(./iii:19): foreach my $num ( @numbers ) {
DB<6> x @test
0 1
1 2
2 3
DB<7> x @numbers
empty array
DB<8> s
main::(./iii:22): push @datawanted, $_;
DB<8> x $num
0 undef
DB<9> s
main::(./iii:23): push @numbers, { map { $_ => 1 } @test };
DB<9> x @numbers
empty array
DB<10> x @test
0 1
1 2
2 3
DB<11> x @_
empty array
DB<12> x $_
0 '1 2 3'
DB<13> s
main::(./iii:23): push @numbers, { map { $_ => 1 } @test };
DB<13> x $_
0 1
DB<14> s
main::(./iii:23): push @numbers, { map { $_ => 1 } @test };
DB<14> x $_
0 2
DB<15> x $_
0 2
DB<16> s
main::(./iii:23): push @numbers, { map { $_ => 1 } @test };
DB<16> x $_
0 3
DB<17> s
main::(./iii:18): my @test = split;
DB<17> s
main::(./iii:19): foreach my $num ( @numbers ) {
DB<17> x @numbers
0 HASH(0xc0b04)
1 => 1
2 => 1
3 => 1
DB<18>
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