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#1
May 7th, 2008, 03:52 PM
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Notations: Grep { /.../ } @array -vs- grep(/.../, @array)
I recall reading from an external source that the notation grep { /.../ } @array offers advantages over the other notation grep(/.../, @array). But I can't find the article any more. Does anyone have anything to say about that?
The only thing I can think of is if you can incorporate some complex expressions in the { } that you can't incorporate into the ( ).
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#2
May 7th, 2008, 04:22 PM
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Nope. { } is actually a code block, so you can put more complex expressions that cannot be evaluated in a single expression.
Basically grep has two forms: grep BLOCK LIST grep EXPR, LIST Note that there is no comma between BLOCK and LIST. For EXPR, you would normally use a simple expression such as: Code:
@array = (1, 2, -1, 3); @array2 = grep $_ > 1, @array; This will pull all elements of @array that are > 1 (i.e.) 2 and 3. By the way, EXPR does not need to be a regular expression either, it can be a simple expression of any kind. This can also be easily implemented as a block with virtually the same syntax: Code:
@array = (1, 2, -1, 3);
@array2 = grep {$_ > 1} @array;
Now if you have something more complex that cannot be achieved in a single expression. Say you have to map some values to some other values according to the following rules: value > 0 and value <= 2: group 1 value > 2 and value <= 5: group 2 value > 5 and value <= 8: group 3 anything else : group 4 To do this mapping with a grep, you would use a block like this: Code:
@array = (1, 5, 2, 6, 10, 4);
@array2 = grep { if ($_ > 0 && $_ <= 2) {
$_ = 1;
}
elsif ($_ > 2 && $_ <= 5) {
$_ = 2;
}
elsif ($_ > 5 && $_ <= 8) {
$_ = 3;
}
else {
$_ = 4;
}
} @array;
You cannot do this sort of logic with a simple expression.
__________________
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#3
May 7th, 2008, 05:46 PM
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I see the point you're making Scorp, but surely the last example is better suited to 'map', so you can create @array2 without altering the values in @array.
__________________
~ishnid; Have you tried: [ search.cpan.org | perldoc | Java API | mysql.com | google ] Apostrophes are NOT used for possessive pronouns or for noun plurals, including acronyms.
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