PHP Arrays for Fun and Profit

UPHPU Meeting
November 17, 2005

Mac Newbold
mac@macnewbold.com

Who am I?
 * Full-time self-employed computer geek
   * Code Greene (www.codegreene.com, partner)
   * Wide variety of PHP/MySQL web sites and applications
   * Fan of FreeBSD, Firefox, Flyspray, etc.
 * Background: B.S. C.S. '01, M.S. C.S. '05
   * University of Utah - Go Utes!

The Plan
 * Array Basics
   * Lists and Associative Arrays
   * Array operators and functions
 * Using Arrays
   * Looping with Arrays
   * Sorting Arrays
   * Using arrays as parameters to functions
 * Data Structures with Arrays

The Array Data Type in PHP
 * www.php.net/manual/en/language.types.array.php
 * Two types: Lists and Associative Arrays
   * Every array is pairs of keys and values
 * Consecutive numeric keys (0-based) is a list
   * Implied when you don't specify any keys
 * Other keys (i.e. strings) is an associative array, a.k.a. hash, map, etc.

Making Arrays
 * $list = array('foo',$bar,"BAZ",1,2,3);
   * List: [0]=>'foo', [1]=>$bar, [2]=>... ... ...
   * echo $list[0];  -> foo
 * $map=array("dog"=>"brown","cat"=>"fat")
   * Associative array: [dog]=>brown, [cat]=>fat
   * echo $map["dog"];  -> brown
 * $list[] = 4;
 * $map["mouse"] = "quiet";

Array Operators
 * 5 for comparison, 1 other
 * ==, !=, <> - Test for [in]equality
   * Same key/value pairs (using "type juggling")
 * ===, !== - Test for identity
   * Same pairs, same order, same types
 * Union: +  (see also array_merge())
   * Numeric keys get reindexed
   * For duplicate keys, left hand dominates

Array Functions
 * Over 75 array functions
 * Some are obvious and self-explanatory:
   * array(), is_array(), unset(), in_array(), count(), shuffle(),
     array_keys(), array_values(), array_reverse(), array_sum(), 
     array_product()
 * array_[push,pop,shift,unshift]()
   * Push and pop at the end
   * Shift (on) or unshift (off) at the beginning

Array Functions 2
 * Set operations: Union, Diff, Intersect
 * array_[u]{diff,intersect}[_[u]{assoc,key}]()
   * Plain: compare values
   * Key: compare keys
   * Assoc: compare values and keys
   * u/uassoc/ukey: Compare with callback function
   * udiff/uintersect: allow recursive/deep compare
 * Rarely need anything but plain, key, assoc

Array Functions 3
 * $str = implode(":",$arr);
 * $arr = explode(":",$str);
 * $arr = array_combine($keys,$values);
 * $arr = array_flip($arr); // val=>key
 * $arr = array_pad($arr_in, 10, "");
 * array_slice, array_splice - cut/paste
 * Extract, compact - array <=> variables

Array Functions 4
 * Array_walk() - apply callback to pairs
 * Array_map() - return array of results of applying callback to pairs
 * Array_unique() - delete duplicate values
 * Array_rand() - choose random key(s)
 * list($first,$second,$third) = $arr;
 * There are a bunch more too...

The Plan
 * Array Basics
   * Lists and Associative Arrays
   * Array operators and functions
 * Using Arrays
   * Looping with Arrays
   * Sorting Arrays
   * Using arrays as parameters to functions
 * Data Structures with Arrays

Looping with Arrays
 * Arrays have internal pointers for iterating
   * Current(), prev(), next(), reset(), end(), key()
   * list($key,$val) = each($arr) - grabs next pair
 * foreach ($arr as $v) { }
 * foreach ($arr as $k => $v) { }
 * while (list($k,$v) = each($arr)) { }
 * for ($i=0; $i<count($arr); $i++) { $arr[$i];}

Sorting Arrays
 * sort() - sort by value
 * ksort() - sort by key
 * asort() - sort by value, keep associations
 * rsort(), krsort(), arsort() - reverse
 * usort(), uksort(), uasort() - custom compare
 * natsort(), natcasesort() - "natural order"
 * shuffle() - You guessed it...

Arrays as Parameters
 * Many string functions can do more complex things when arrays are
   used as parameters:
   * $arr = array('foo','bar');
   * str_replace($arr,"baz",$str);
   * str_replace($arr,array('blah','boo'),$str);
 * Passing arrays by reference lets you "return" multiple values from
   a function:
   * function getUser(&$result) { }

Arrays as Return Values
 * Rather than returning by reference, you can simply return an array directly:
   * return array("rv1"=>17,"rv2"=>42);
 * Many standard functions return arrays:
   * MySQL for example: mysql_fetch_*()
   * Assoc gets associative, row gets numeric, array gets either, or
     both at once
 * Remember: list($rv1, $rv2) = getPair();

Data Structures with Arrays
 * Plain arrays already do a whole lot:
   * List, vector, hash, map, set, stack, queue, etc.
 * Trees and recursive structures are easy:
   * Multi-dimensional arrays: $arr[3][7][9];
   * Hash/map of arrays - $arr["person1"]["name"]
 * "Struct" (a la C) or "mock object"
   * $obj = array("name"=>"joe", "age"=>"64");
   * Quicker/simpler than going fully OOP

Arrays and HTTP/HTML
 * Make arrays with GET or POST variables:
   * index.php?list[0]=foo&list[1]=bar
   * index.php?list[]=blah&list[]=hm&list[]=wow
 * HTML Forms for arrays:
   * <input name="person[name]">
   * <input type="checkbox" name="list[yes]">
   * <select multiple name="choices[]">
   * Always use [] for multiple select - the only way 

Grand Finale
 * Arrays are pretty simple, yet incredibly powerful at the same time. 
   They're well worth any time you invest in learning to use them well. 

 * Any questions?