Beefy Boxes and Bandwidth Generously Provided by pair Networks
Syntactic Confectionery Delight
 
PerlMonks  

comment on

( #3333=superdoc: print w/replies, xml ) Need Help??
Let's say you have two lists, @a and @b, and all elements of @b are contained in @a. How do you get "@a without @b"? Of course, one could sort both lists, iterate through the elements of @a, have an index for @b, and push elements in @a to an array @c if the element in @a is not at that position in @b. But that seems rather tedious. For instance,
@b = sort {$a <=> $b} @b; @a = sort {$a <=> $b} @a; print "@b\n"; for (@a) { if (defined($b[$i])) { if (not $_ == $b[$i]) { push @c, $_ } else { $i++ } } else { push @c, @a[($j..$#a)]; last; } $j++; }

I'm sure this can be done in a somewhat more efficient (perl-ish *g) way ... like this:
@c = grep { defined($b[0]) and !($b[0] eq $_) or !shift @b } sort {$a <=> $b} @a;

This should work if @b is already sorted. I'm sure it can be done in better ways .. I'm brand-new at Perl after all.

John

In reply to most efficient way to implement "A without B" by telcontar

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, 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, 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.
  • Log In?
    Username:
    Password:

    What's my password?
    Create A New User
    Chatterbox?
    and the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others chanting in the Monastery: (3)
    As of 2020-05-26 10:52 GMT
    Sections?
    Information?
    Find Nodes?
    Leftovers?
      Voting Booth?
      If programming languages were movie genres, Perl would be:















      Results (150 votes). Check out past polls.

      Notices?