perl push many array in one array

Question

I have many short array

 @seq1 /773..1447/        @seq2 /1 2 1843..1881 1923..2001/

but i use push

   push(@add, @seq1);
   push(@add, @seq2);

but it shows like it combine all array into one can't get each sub-array any more

  /773..1447 1 2 1843..1881 1923..2001/

when i use

  $number=@add;

it shows 6, but it should be 2. Can anyone explain the reason and how to change it.

When i use for loop to add each array

   for(..){
 @temp= split(/,/,$_); 
 push(@add, \@temp);
 }

Then when i print @add; it only shows memory address, How can show all data in @add

You really need to read perldoc perllol.

Dave Cross
– Dave Cross

2014-02-12 10:41:18 +00:00
Commented Feb 12, 2014 at 10:41 — Dave Cross
– Dave Cross, Commented Feb 12, 2014 at 10:41

mpapec · Accepted Answer · 2014-02-12 07:10:15Z

7

This is normal behavior, use reference to @seq1 if you want @add to be two dimensional array,

push(@add, \@seq1);

To print all values in @add you should use Data::Dumper; print Dumper \@add;

The reason is that all parameters get flattened into list when they are pushed into array, so

@a = @b = (1,2);
push(@add, @a, @b);

is same as writing

push(@add, $a[0],$a[1], $b[0],$b[1]);

Check perlref and perllol for reference.

edited Feb 12, 2014 at 7:10

answered Feb 12, 2014 at 6:46

mpapec

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Comments

vanHoesel · Accepted Answer · 2014-02-12 18:00:07Z

the push command takes an ARRAY and a LIST. It is important to understand what happens here.

The first argument must be an ARRAY, the one you want to push things on. After that it expects a LIST. What this means is that this push statement provides list context to any @seq_n array - and sort of expands the array into separate elements. So all the elements of the @seq_n are being pushed onto your @add.

Since you did not want that to happen, you wanted an array that holds the separate lists - what we call in Perl a List-of-Lists - you actually wanted to push a reference to your @seq_n arrays, using the \ character.

push @add, \@seq_1, \@seq_2, . . . \@seq_n;

Now you have an array that indeed holds references to each $seq_n.

To print them neatly, each sequence on its own line, you could iterate over each

foreach my $seq (@add) {
  # $seq holds a reference to a list!
  my $string = join " ", @$seq; # the @ dereferences the $seq
  print $string, "\n";
}

but TIMTOWTDI

print map {(join " ", @$_), "\n"} @add;

Always consider the context in Perl, and try to embrace the charms of join, grep and map.

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