Re: Comparing arrays

Update: In deference to Arien's concerns.

if ( do{ local$"=''; @array1 == @array2 and "@array1" eq "@array2"} ) 
+{ 
    print 'They are the same', $/; 
}
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Which of course will also break if you have two arrays,

my @a = ( 'onetwo','', 'three');
my @b = ( 'one', 'two', 'three' );
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And as with any shortcuts, you need to know your data before you apply them. If your not comforable with that, don't use it.

Update more:

I'll spell it out for those unable or unwilling to make the mental leap for themselves.

If your data is wholey numeric, then use $"=<any non-numeric-char>.

If your data consists of wholey alpha data use a non-alpha char.

If your data consists of mixed alpha-numeric then use a non-alpha-numeric.

If your data can contain any char in the range 32-127, cosider using a control character (eg."\cA").

If your data can contain any 7-bit char, use an 8-bit char. 128-255.

If there is simply no character that your data does not contain, then you need to compare element-by-element. These cases are very rare. In almost all normal sets of data it is possible to find a single char that you can get away with using, and eq testing of the stringyfied arrays is a simple, and efficient way of performing this kind of test on small datasets.

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Re: Re: Comparing arrays by Arien (Pilgrim) on Dec 24, 2002 at 09:32 UTC
That doesn't necessarily work as intended if the values of one or more elements in either array contain the list separator `$"`: `my @array1 = qw(one two three); my @array2 = ("one" . $" . "two", "three"); if ("@array1" eq "@array2") { print 'They are the same', $/; # no, they are NOT }` [download] The updated code is still flawed, consider: `my @array1 = qw(one two three); my @array2 = qw(onetwo three); if ( do{ local $" = ''; "@array1" eq "@array2"} ) { print 'They are the same', $/; # no, they are NOT }` [download] This second update still isn't the way to do it... I took out the `local $"` (which should be no problem as the value of `$"` shouldn't matter anyway). Consider: `my @array1 = ("one", "two" . $" . "three"); my @array2 = ("one" . $" . "two", "three"); if ( do{ @array1 == @array2 and "@array1" eq "@array2"} ) { print 'They are the same', $/; # no, they are NOT }` [download] Stringifying would only work if it is guaranteed that `$"` doesn't occur as a substring of one or more values of either array. — Arien	[reply] [d/l] [select]

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Re: Re: Comparing arrays
by Arien (Pilgrim) on Dec 24, 2002 at 09:32 UTC

That doesn't necessarily work as intended if the values of one or more elements in either array contain the list separator $":

my @array1 = qw(one two three);
my @array2 = ("one" . $" . "two", "three");

if ("@array1" eq "@array2") {
    print 'They are the same', $/;   # no, they are NOT
}
[download]

The updated code is still flawed, consider:

my @array1 = qw(one two three);
my @array2 = qw(onetwo three);

if ( do{ local $" = ''; "@array1" eq "@array2"} ) {
    print 'They are the same', $/;   # no, they are NOT
}
[download]

This second update still isn't the way to do it... I took out the local $" (which should be no problem as the value of $" shouldn't matter anyway). Consider:

my @array1 = ("one", "two" . $" . "three");
my @array2 = ("one" . $" . "two", "three");

if ( do{ @array1 == @array2 and "@array1" eq "@array2"} ) { 
    print 'They are the same', $/;    # no, they are NOT
}
[download]

Stringifying would only work if it is guaranteed that $" doesn't occur as a substring of one or more values of either array.

— Arien

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