I know this is a FAQ, and I know the answer(s) in the FAQ.
.
.
. 
index ("@array", $sought) > -1;

[download]

Please note, however, that isn't one of the suggested methods that is in the FAQ. ;-)

I disagree with the FAQ in this case. Often, grep is exactly what you want. If grep isn't good enough, then you probably chose the wrong data structure in the first place. (The FAQ also shows a C-ish example of hopping out of a loop when an element is found. Even though that halves your number of comparisons on average, it's still O(N); given that grep is quick, for small arrays, it probably isn't worth it.)

As far as doing it this way, well... you've already gotten some responses that outline the issues. As dws said, if it is a single character you are looking for, then no problem. (What he didn't mention was that if it is a single character you are looking for, then you might be better off using tr// instead of index().)

You can use it for longer data if you no a particular substring will never show up in the data. For obvious reasons, it's best if that substring is short, like a single character. A good choice might be "\0". Once you choose your substring, you have to set $" appropriately and you still have to be careful...Some examples of what to watch for: 

@a = qw( food bar baz );
$" = "\0"; 
print "Found\n" if index "@a", qq/foo/;     # Wrongly succeeds.
print "Found\n" if index "@a", qq/foo$"/;   # Rightly fails.
print "Found\n" if index "@a", qq/$"bar$"/; # Rightly succeeds...
print "Found\n" if index "@a", qq/$"baz$"/; # Wrongly fails.

[download]
Here's how to make it work: 
print "Found\n" if index qq($"@a$"), qq/$"foo$"/;

[download]
In words, you have to tack the delimiter on to both the front and back of both the string you are searching through and the one you are searching for.

Not only is it a mess, stringifying the array might use a lot of memory if the array is big... and if the array isn't big, you aren't really buying yourself much.

Conclusion: In most cases, grep will do fine. If it won't choose a better data structure. If that isn't an option, write a loop and bail out after finding the first match. But there's no good reason to use index on a stringified array, IMHO.

-sauoq
"My two cents aren't worth a dime.";

In reply to Re: Is X in my array? by sauoq
in thread Is X in my array? by Not_a_Number

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.