Looping through all the keys in the hash is very inefficient. To check if $name is a key of %$all_names, you could use :

exists $$all_names{$name};
%$all_names ~~ $name; # Shortcut using the smartmatch operator

[download]

Note that this isn't the same as defined $$all_names{$names}. If you do $$all_names{$key} = undef, exists would return true (because the key exists), but defined would return false (because the value is undefined).

To select elements from an array based on a condition, you can use grep { condition } @array. Putting it all together, to get all elements of @arr_of_names that are keys of %$all_names, you can try this :

@good = grep { %$all_names ~~ $_ } @arr_of_names;

[download]

Note that inside the grep condition, the element being tested is aliased to $_.

In reply to Re: Finding hash keys in array by Grimy
in thread Finding hash keys in array by Anonymous Monk

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.