Perl Two-dimensional arrays

"Reprint" Source: http://www.cnblogs.com/visayafan/

• 1 Arrays and references
• 2 Differences of the statements
• 3 Differences in Access
• 4 Adding row elements
• 5 Adding column elements
• 6 Accessing and printing
  • 6.1 Operator Precedence
  • 6.2 Visit A
  • 6.3 Traversal
• 7 slices

1 arrays and references

This refers to pointers in C equivalent.
The first column of a two-dimensional array stores a reference to a one-dimensional array of that row instead of storing the concrete element.

2 Differences of the statements

• The array is declared in the following form:
  Add @ before the array name, followed by ().
  

  
  

my @AoA = (
           [ "fred", "barney", "pebbles", "bambam", "dino", ],
           [ "george", "jane", "elroy", "judy", ],
           [ "homer", "bart", "marge", "maggie", ],
          );

• The following form of declaration is quoted:
  Use $ before the reference name, followed by [].
  

  
  

$ref_to_AoA = [
               [ "fred", "barney", "pebbles", "bambam", "dino", ],
               [ "george", "jane", "elroy", "judy", ],
               [ "homer", "bart", "marge", "maggie", ],
              ];

3 differences in Access

• Array access
  

  
  

$AoA [$i] [$j]

Because the first column array contains references, you can also access this:

$AoA [$i]->[$j]

• Reference access
  

  
  

$ref _aoa->[$i [$j]

Similarly, references can be accessed in this way:

$ref _aoa->[$i]->[$j]

4 adding row elements

My (@AoA, $ref_to_AoA);

Sub print_AoA{
     For (@AoA) {
         Print "@{$_}\n";
     }
     Print "\n";
}

# assign to our array, an array of array references
@AoA = (
            [ "fred", "barney", "pebbles", "bambam", "dino", ],
            [ "george", "jane", "elroy", "judy", ],
            [ "homer", "bart", "marge", "maggie", ],
           );
Say $AoA[2][1];

$ref_to_AoA = [
                [ "fred", "barney", "pebbles", "bambam", "dino", ],
                [ "george", "jane", "elroy", "judy", ],
                [ "homer", "bart", "marge", "maggie", ],
               ];
print_AoA();

My @tmp = (1, 2, 3, 4);
Push @AoA, [@tmp]; # Because the first column of the array AoA needs a reference, and @tmp is an array, the direct assignment will be wrong. [] means to return a reference to @tmp, that is, push the reference of @tmp to the last line of @AoA, and increase the number of rows of the two-dimensional array by 1.
print_AoA();

Push @AoA, @tmp;
print_AoA();

Overwrite rows

#$AoA[0] = @tmp; #$AoA[0] is a scalar type, and @tmp is a list type, so by default the number of tmp is assigned to $AoA[0], ie $AoA[0]= 4;
$AoA[0] = [@tmp]; #overwirte
print_AoA();

5 Adding column elements

Push @{$AoA [0]}, "Wilma", "Betty";

Omit @{}

Use v5.14; # needed for implicit deref of array refs by array ops
Push $AoA[0], "wilma", "betty"; # Cannot pass before version 5.14, because the first parameter of push must be an array. In the new version, there is a reference in $AoA[0], but it is incorrect when there is no reference.
print_AoA();
My $aref = undef;
#push $aref, qw/some value/; # ERROR: Not an ARRAY reference
My $aref = [@tmp];
Push $aref, qw/some value/; # correct, because aref is not a null reference at this time
Print "$aref : @$aref\n";

6 Accessing and printing6.1 Operator Precedence

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6.2 Visit a

Print $AoA [$i] [$j];p rint ref_$aoa->[$i]->[$j];

6.3 Traversal

• The simplest kind of
  

  
  

For $aref ( @AoA ) # $aref is just a reference in the first column. To access the entire line, you must add @, and the $ access level is higher than @, so () can be omitted.
{
     Say "\t [ @$aref ],";
}

• Using $#
  

  
  

For my $i (0: $ #AoA) {    say "Elt $i is @{$AoA [$i]}";}

• Inline loops
  

  
  

for my $i (0 .. $#AoA){
    for my $j (0 .. $#{$AoA[$i]}){
        say "elt $i, $j is $AoA[$i][$j]\n";
    }
}

7 slices

To access several rows of several columns of elements. and MATLAB to access the matrix in the same way.

• Cut single-row multiple columns
  

  
  

My @part = ();
My $x = 4;
For (my $y = 1; $y<4; $y++){
     Push @part, $AoA[$x][$y];
}  @part = @{$AoA[4]}[1..4];

• Cut multi-row multiple columns
  

  
  

My @newAoA = ();
For (my $startx= my $i = 1; $i<=5; $i++){
     For(my $starty = my $j = 2; $j<=4; $j++){
         $newAoA[$i - $startx][$j - $starty] = $AoA[$i][$j];
     }
}

#a simple cycle
For (my $x = 1; $x<=5; $x++){
     Push @newAoA, [@{$AoA[i]}[2 .. 4]];
}

• Writing functions
  

  
  

sub splice_2D{
    my $lrr = shift;
    my($x_l, $x_h,
       $y_l, $y_h) = @_;
    return map(
               [ @{$lrr -> [$_]} {$y_l .. $y_h}]
              )$x_l .. $x_h;
}
@newAoA = splice_2D(\@AoA, 1=>5, 2=>4);

Author:visaya fan <visayafan[at]gmail.com or visayafan[at]163.com>

date:2011-10-29 15:00:34

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Perl Two-dimensional arrays