Mastering Perl for Bioinformatics [Electronic resources] نسخه متنی

A.6 Arrays

Arrays are ordered
collections
of zero or more scalar values, indexed by position. An array variable
begins with the @ sign followed by a legal
variable name. For instance, here are two possible array variable
names:

@array1
@dna_fragments

You can assign scalar values to an array by placing
the scalar values in a list separated by commas and surrounded by a
pair of parentheses. For instance, you can assign an array the empty
list:

@array = (  );

or one or more scalar values:

@dna_fragments = ('ACGT', $fragment2, 'GGCGGA');

Notice that it's okay to specify a scalar variable
such as $fragment2 in a list. Its current value,
not the variable name, is placed into the array.

The individual scalar values of an array (the elements) are
indexed by their position in
the array. The index numbers begin at 0. You can specify the
individual elements of an array by preceding
the array name by a $ and following it with the
index number of the element within square brackets, like so:

$dna_fragments[2]

This equals the value of 'GGCGGA', given the
values previously set for this array. Notice that the array has three
scalar values indexed by numbers 0, 1, and 2. The third and last
element is indexed 2, one less than the total number of elements 3,
because the first element is indexed number 0.

You can make a
copy
of an array using an assignment operator =, as in
this example that makes a copy @output of an
existing array @input:

@output = @input;

If you evaluate an array in scalar
context, the value is the number of elements in the array. So if
array @input has five elements, the following
example assigns the value 5 to $count:

$count = @input;

Figure A-1 shows an array
@myarray with three elements, which demonstrates
the ordered nature of an array by which each element appears and can
be found by its position in the array.

You can make a reference to an array by preceding it with a
backslash; you dereference it by preceding the reference with an at
sign @ for the entire array or with an extra
dollar sign $ for an individual element of the
array:

@a = ( 'one', 'two', 'three');
$aref = a;
print $aref, "\n";
print $$aref[0], "\n";
print "@$aref", "\n";

gives the output:

ARRAY(0x811d1e0)
one
one two three

You can also define an array as an anonymous array. An anonymous
array isn't saved in a named array variable;
it's a reference to array data and can only be saved
in a reference. It's initialized within square
brackets:

$anonarray = [ 'one', 'two', 'three'];
print "@$anonarray", "\n";

gives the output:

one two three