_learning perl_, ch15, 14.I.2002, nh

OTHER DATA TRANSFORMATION


finding a substring
~~~~~~~~~~~~~~~~~~~
  if within a bigger string, use `index`:
    $x = index($string,$substring);    
     |
     `-> returns index value of place found in string -- at
         beginning, you get '0'.  after 1st ch, '1'.  &c.
         (returns -1 if no match)
     |
     `-> can take 3rd parameter -- leftmost limit at which to start
         searching
     |
     `-> find right-most occurrence using `rindex`
         (also can take 3rd-parameter index, for >= instead of <=)

extracting and replacing a substring
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  substr(<string><start><length>)
  -------------------------------
  - use it if you know where the substring you want is in the string
  - negative start value counts back from end
  - omitting length is same as making it a ridiculously huge #
  - can also go on left side of assignment operator:
        $hw = "hello world!";
        substr($hw,0,5) = "hey"; # $hw is now "hey world!"
     (length of replacement text doesn't have to be the same)


formatting data wiht sprintf()
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  sprintf() = printf() except that it returns the formatted data
  as one string -- "String printf()"
      $string = sprintf("%5d %8s", $x, $otherstring);

advanced sorting
~~~~~~~~~~~~~~~~
  `sort` already sorts by ASCII value
  must compare values numerically, two at a time:
    sub by_numer {
      return -1 if ($a < $b);
      return 0 if ($a == $b);
      return 1 if ($a > $b);
    }
  @list = sort by_number @wronglist;

* special operator: 'spaceship operator': <=>
    sub by_number {
      $a <=> $b;
    }

  can also do:
  @rightlist = sort { $a <=> $b } @wronglist;

  spaceship is for numeric; `cmp` is for strings

  both numeric and non- at the same time:

    sub mostly_by_number {
      ($a <=> $b) || ($a cmp $b);
    }


transliteration
~~~~~~~~~~~~~~~
  `tr`  -- transliterates, instead of just substituting
  ^^^^
    tr/ab/ba/;    # just like shell `tr ab ba`
    
    syntax: tr/<oldstring>/<newstring>/

    $_ = "fred and barney";
    tr/fb/bf/;              # $_ now = "bred and farney"
    tr/a-z/A-Z/;            # $_ now = "BRED AND FARNEY"
    
  * if new string is shorter,