ITEC 325 2011fall ibarland

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lect04c-arrays
PHP arrays
chapter 7

From PHP Visual Quickstart Guide by Larry Ullman
Originally based on notes by Jack Davis (jcdavis@radford.edu)

• We've already seen: Creating arrays in PHP
  • $list = array('apples', 'bananas','oranges'); The array has indices 0,1,2.
  • $list = array(1=>'apples', 2=>'bananas','oranges'); The array has indices 1,2,3; if index isn't explicitly listed then use the next largest number.
  • associative array

    $soups = array('Monday'=> 'clam chowder', 'Tuesday' => 'vegetable', 'Wednesday' => 'chicken noodle');

  • The range function returns and array with integer indices and contents from a continuous range.

    print_r( range(5,10) ); print_r( range('a','z') ); print_r( range(0,100,3) ); // Indices [0,33]; last value is 99.

• We've already seen: To print an array, use the function print_r: e.g. print_r($soups);. Its output is geared for programmers. ALso, you'll probably want to wrap it inside <pre>…</pre> to keep the browser from ignoring newlines carefully printed by print_r.
• Adding, deleting, accessing array elements
  
  • $list[] = 'pears'; # adds array element to next index with value 'pears'
  • $list[100] = 'grapes'; # sparse arrays
  • unset($list[100]); # deletes one element
  • unset($list); # deletes entire array
• Built in Super Global Arrays (Associative Arrays)
  • $_POST, $_GET, $_REQUEST
  • $_COOKIE
  • $_SERVER
  • $_SESSION
  • $_ENV
• Array Operators
  • count($soups); # returns the no. of elements in array soups - 3
  • sizeof($soups); # alias of count() function
  • print "The first item is $array['total']" # php's transclusion fails¹ ; instead use braces:
    print "The first item is {$array['total']}"; # use braces
  • $new_array = array-merge($array1,$array2); # new array has elements of both This function returns a new array (not pass-by-value); it condenses all the numeric indices so they start from zero (that is, it de-sparsifies it). Note that array_merge is somewhat inconsistent: If $array1[5]=99 and $array2[5]=88, the result will contain both 88 and 99 (each with some numeric key). However, if $array1['five']='ninety-nine' and $array2['five']='eighty-eight', then only one of values 'ninety-nine','eighty-eight' will be in the resulting merged array. (It will still be associated with the key 'five'.)
• Looping through arrays: Preferably, use foreach.
  • If we only want to work with each stored value (don't care about what key it's stored with):

    foreach($array as $val) { statements… }

    Note that $array must be declared before the loop of course, but $val is (essentially) a temporary variable used just for the loop itself.
  • If we care about the key each value is stored at:

    foreach ($myArray as $key => $val) { statements… }

    (works for associate arrays, as well as numeric indices whether or not it's sparse).
    Again, both the variables $key and $val are to be thought of as local variables, introduced for the purpose of the loop.

  • It is also possible to use a regular for-loop or while-loop as in Java etc., but it is preferred to use a foreach loop when possible.

    Note that for sparse arrays (i.e. skipped numeric indices), a conventional for/while loop will not do what presumably you want:

    $data = array(17,18, 4=>21, 44 => 51, 52); /* array( 0 => 17 ,1 => 18 ,4 => 21 ,44 => 51 ,45 => 52 ) */ for ($i=0; $i < sizeof($data); ++i) { …$data[$i]… // $data[$i] ranges over: 17, 18, NULL, NULL, 21, NULL. }

• Multidimensional Arrays: ch07-books.php
• Sorting Arrays
  • ch07-array-example.php
  • ch07-assoc-array-example.php

  • Array Sorting Function
    Function	sorts by…	Maintains key-value associations?
    sort	values	no
    rsort	values (reverse)	no
    asort	values	yes
    arsort	values (reverse)	yes
    ksort	keys	yes
    krsort	keys (reverse)	yes

    Note that there is something non-standard about sorting an array, w/o changing the key-value pairs: the (associative) array has an ordering aside from the order of the keys?!
    • natsort (and it's case-insensitive cousin natcasesort) sort an array of alphanumeric strings using a “natural order”: "image23.jpg" comes before "image125.jpg"(!). However, non-alphanumeric characters will goof it up: "image_23" comes after image_125, making this function eminently more pitfall-ful (or at the least, less helpful).
    • usort, uasort, ursort — sort an array using a user-defined comparison function.
      (You pass in a string that is the name of a comparison function.)
    Note that all the built-in sort functions don't return a sorted array — they return true and they use pass-by-reference, so they must be passed a variable (not any other array expression: sort( array('hi','bye') ) is an error.
  • Forms using arrays effectively: If several (input) elements have the same name attribute ending in “[]” (say, “someInfo[]”), then the receiving $_POST value is an array (that is, $_POST['someInfo'] is an array).
    ch07-forms-with-arrays-enter.php
    Beware checkboxes, where if none of the elements named someinfo[] were selected then $_POST['someInfo'] won't be an empty array — it will be null.

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©2011, Ian Barland, Radford University Last modified 2011.Dec.07 (Wed)

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