PHP - Introduction to PHP Arrays

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PHP Bible, 2nd
Edition 1 © Wiley and the book authors, 2002

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PHP Bible, 2nd
Introduction to
PHP Arrays

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PHP Bible, 2nd
SummarySummary
• How arrays work in PHP
• Using multidimensional arrays
• Imitating other data structures with arrays
• Sorting and other transformations

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PHP Bible, 2nd
Uses of ArraysUses of Arrays
• Arrays are definitely one of the coolest and most flexible
features of PHP. Unlike vector arrays from other
languages (C, C++, etc.), PHP arrays can store data of
varied types and automatically organize it for you in a
large variety of ways.
• Some of the ways arrays are used in PHP include:
o Built-in PHP environment variables are in the form of arrays (e.g. $_POST)
o Most database functions transport their info via arrays, making a compact
package of an arbitrary chunk of data
o It's easy to pass entire sets of HTML form arguments from one page to another
in a single array
o Arrays make nice containers for doing manipulations (sorting, counting, etc.)
of any data you develop while executing a single page's script

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PHP Bible, 2nd
What are PHP arraysWhat are PHP arrays
• PHP arrays are associative arrays with a little extra thrown in.
• The associative part means that arrays store element values in
association with key values, rather than in a strict linear index
order
• If you store an element in an array, in association with a key,
all you need to retrieve it later from that array is the key value
o $state_location['San_Mateo'] = 'California';
o $state = $state_location['San_Mateo'];
• If you want to associate a numerical ordering with a bunch of
values or just store a list of values, all you have to do is use
integers as your key values
o $my_array[1] = 'The first thing';
o $my_array[2] = 'The second thing';

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PHP Bible, 2nd
Associative vs. vectorAssociative vs. vector
arraysarrays
• In vector arrays (like those used in C/C++), the contained
elements all need to be of the same type, and usually the
language compiler needs to know in advance how many
such elements there are likely to be
o double my_array[100]; // this is C
• Consequently, vector arrays are very fast for storage and
lookup since the program knows the exact location of each
element and they are stored in a contiguous block of memory
• PHP arrays are associative (and may be referred to as hashes)
• Rather than having a fixed number of slots, PHP creates array
slots as new elements are added to the array and elements
can be of any PHP type

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PHP Bible, 2nd
Creating arraysCreating arrays
• There are 4 main ways to create arrays in PHP
o Direct assignment
• Simply act as though a variable is already an array and assign a value into
it
$my_array[1] = 1001;
o The array() construct
• Creates a new array from the specification of its elements and associated
keys
• Can be called with no arguments to create an empty array (e.g. to pass
into functions which require an array argument)
• Can also pass in a comma-separated list of elements to be stored and the
indices will be automatically created beginning with 0
$fruit_basket = array('apple','orange','banana','pear');
o Where $fruit_basket[0] == 'apple', $fruit_basket[1] == 'orange', etc.

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PHP Bible, 2nd
Creating arrays (cont.)Creating arrays (cont.)
o Specifying indices using array()
• If you want to create arrays in the previous manner but specify the indices
used, instead of simply separating the values with commas, you supply
key-value pairs separated by commas where the key and the value are
separated by the special symbol =>
$fruit_basket = array ('red' => 'apple',
'orange' => 'orange',
'yellow' => 'banana',
'green' => 'pear');
o Functions returning arrays
• You can write your own function which returns an array or use one of the
built-in PHP functions which return an array and assign it to a variable
$my_array = range(6,10);
o Is equivalent to
$my_array = array(6,7,8,9,10);
o Where $my_array[0] == 6;

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PHP Bible, 2nd
Retrieving valuesRetrieving values
• The most direct way to retrieve a value is to use its
index
o If we have stored a value in $my_array at index 5, then $my_array[5] will
retrieve that value. If nothing had been stored at index 5 or if $my_array
had not been assigned, $my_array[5] will behave as an unbound variable
• The list() construct is used to assign several array
elements to variables in succession
$fruit_basket = array('apple','orange','banana');
list($red_fruit,$orange_fruit) = $fruit_basket;
o The variables in list() will be assigned the elements of the array in the
order they were originally stored in the array

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PHP Bible, 2nd
Multidimensional arraysMultidimensional arrays
• The arrays we have looked at so far are one-dimensional
in that they only require a single key for assigning or
retrieving values
• PHP can easily support multiple-dimensional arrays, with
arbitrary numbers of keys
o Just like one-dimensional arrays, there is no need to declare our intensions in
advance, you can just assign values to the index
$multi_array[1][2][3][4][5] = 'deep treasure';
• Which will create a five-dimensional array with successive keys that
happen, in this case, to be five successive integers
• It may be easier to consider that the values stored in
arrays can themselves be arrays.
$multi_level[0] = array(1,2,3,4,5);
• Where $multi_level[0][0] == 1 and $multi_level[0][1] == 2

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PHP Bible, 2nd
Multidimensional arraysMultidimensional arrays
(cont.)(cont.)
$cornucopia = array('fruit' => array('red' => 'apple',
'orange' => 'orange',
'yellow' => 'banana',
'green' => 'pear'),
'flower' => array('red' => 'rose',
'yellow' => 'sunflower',
'purple' => 'iris'));
$kind_wanted = 'flower';
$color_wanted = 'purple';
print("The $color_wanted $kind_wanted is {$cornucopia[$kind_wanted]
[$color_wanted]}");
• Would print the message "The purple flower is iris"

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PHP Bible, 2nd
Deleting from arraysDeleting from arrays
• Deleting an element from an array is just like getting
rid of an assigned variable calling the unset()
construct
unset($my_array[2]);
unset($my_other_array['yellow']);

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PHP Bible, 2nd
IterationIteration
• Iteration constructs provide techniques for dealing with
array elements in bulk by letting us step or loop through
arrays, element by element or key by key
• In addition to storing values in association with their keys,
PHP arrays silently build an ordered list of the key/value
pairs that are stored, in the order that they are stored for
operations that iterate over the entire contents of the
array
• Each array remembers a particular stored key/value pair
as being the current one, and array iteration functions
work in part by shifting that current marker through the
internal list of keys and values
o This is commonly referred to as the iteration pointer, although PHP does not
support full pointers in the sense that C/C++ programmers may be used to

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PHP Bible, 2nd
Our favorite iterationOur favorite iteration
method:method: foreachforeach• Our favorite construct for looping through an array is foreach which is
somewhat related to Perl's foreach, although it has a different syntax
• There are 2 flavors of the foreach statement
o foreach (array_expression as $value_var)
• loops over the array given by array_expression. On each loop, the value of the
current element is assigned to $value_var and the internal array pointer is
advanced by one (so on the next loop, you'll be looking at the next element)
o foreach (array_expression as $key_var => $value_var)
• does the same thing, except that the current element's key will be assigned to
the variable $key_var on each loop
• array_expression can be any expression which evaluates to an array
• When foreach first starts executing, the internal array pointer is automatically
reset to the first element of the array. This means that you do not need to call
reset() before a foreach loop

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PHP Bible, 2nd
foreachforeach exampleexample
• If you would like to see each of the variables names
and values sent to a PHP script via the POST
method, you can utilize the foreach construct to
loop through the $_POST array
print ('<TABLE><TR><TH>Name</TH>'.
'<TH>Value</TH></TR>');
foreach ($_POST as $input_name => $value)
{
print ("<TR><TH>$input_name</TH>".
"<TD>$value</TD></TR>n");
}
print ('</TABLE>');

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PHP Bible, 2nd
Iterating withIterating with current()current()
andand next()next()
• foreach is useful in situations where you want to simply loop through an array's values
• For more control, you can utilize current() and next()
• The current() function returns the stored value that the current array pointer is pointing
to
o When an array is newly created with elements, the element pointed to will always
be the first element added
• The next() function advances the array pointer and then returns the current value
pointed to
o If the pointer is already pointing to the last stored value, the function returns false
o If false is a value stored in the array, next will return false even if it has not reached
the end of the array
• To return the array pointer to the first element in the array, use the reset() function

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PHP Bible, 2nd
Reverse order withReverse order with end()end()
andand prev()prev()
• Analogous to reset() (which sets the array pointer to the
beginning of the array) and next() (which sets the array
pointer to the next element in the array and returns its value)
are end() and prev()
o end() moves the pointer to the last element in the array and returns its value
o prev() moves the pointer to the previous element in the array and returns its value
• Another function designed to work with iterating through
arrays is the key() function which returns the associated key
from the current array pointer
• Note: when passing an array to a function - just like other
variables - only a copy of the array is passed, not the original.
Subsequent modifications to the array's values or its pointer will be
lost once the function returns unless the array is passed by
reference

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PHP Bible, 2nd
Empty values and theEmpty values and the
each() functioneach() function
• One problem with utilizing the next function to determine when
the end of the array has been reached is if a false value or a
value which is evaluated to be false has been stored in the array
$my_array = array(1000,100,0,10,1);
print (current($my_array));
while ($current_value = next($my_array))
print ($current_value);
o Will stop executing when reaching the third element of the array
• The each() function is similar to next() except that it returns an
array of information instead of the value stored at the next
location in the loop. Additionally, the each() function returns the
information for where the pointer is currently located before
incrementing the pointer
o The each() function returns the following information in an array
• Key 0/'key': the current key at the array pointer
• Key 1/'value': the current value at the array pointer

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PHP Bible, 2nd
each()each() exampleexample
• To use each to iterate through the $_POST array:
print ('<TABLE><TR><TH>Name</TH>'.
'<TH>Value</TH></TR>');
reset ($_POST);
while ($current = each($_POST))
{
print ("<TR><TH>{$current['key']}</TH>".
"<TD>{$current['value']}</TD></TR>n");
}
print ('</TABLE>');

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PHP Bible, 2nd
Transformations of arraysTransformations of arrays
• PHP offers a host of functions for manipulating your data
once you have nicely stored it in an array
o The functions in this section have in common is that they take your array, do
something with it, and return the results in another array
• array array_keys (array input [,mixed search_value])
returns the keys, numeric and string, from the input array.
o If the optional search_value is specified, then only the keys for that value are
returned. Otherwise, all the keys from the input are returned.
• array array_values ( array input) returns all the values
from the input array and indexes numerically the array
o Simply returns the original array without the keys

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PHP Bible, 2nd
More arrayMore array transformationtransformation
functionsfunctions• array array_count_values ( array input) returns an array using the
values of the input array as keys and their frequency in input as values
o In other words, array_count_values takes an array as input and returns
a new array where the values from the original array are the keys for the
new array and the values are the number of times each old value
occurred in the original array
• array array_flip ( array trans) returns an array in flip order, i.e. keys
from trans become values and values from trans become keys
o Although array keys are guaranteed to be unique, array values are not.
Consequently, any duplicate values in the original array become the
same key in the new array (only the latest of the original keys will survive to
become the new values)
o The array values also have to be integers or strings. If values which cannot
be converted to keys are encountered, the function will fail and a
warning will be issues

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PHP Bible, 2nd
More arrayMore array transformationtransformation
functionsfunctions• array array_reverse ( array array [, bool preserve_keys])
takes input array and returns a new array with the order of the elements
reversed, preserving the keys if preserve_keys is TRUE
• void shuffle ( array array) shuffles (randomizes the order of the
elements in) an array
o Note: calls to srand prior to shuffle is no longer necessary
o Unlike most functions, shuffle actually modifies the original array
and does not return a value
• array array_merge ( array array1, array array2 [,
array ...]) merges the elements of two or more arrays together so
that the values of one are appended to the end of the previous one. It
returns the resulting array
o If the input arrays have the same string keys, then the later value for
that key will overwrite the previous one. If, however, the arrays
contain numeric keys, the later value will not overwrite the original
value, but will be appended

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PHP Bible, 2nd
SortingSorting
• PHP offers a host of functions for sorting arrays
o As we saw earlier, a tension sometimes arises between respecting the
key/value associations in an array and treating numerical keys as
ordering info that should be changed when the order changes
o PHP offers variants of the sorting functions for each of these behaviors
and also allows sorting in ascending or descending order and by
user-supplied ordering functions
• Conventions used in naming the sorting functions include:
o An initial a means that the function sorts by value but maintains the
association between key/value pairs the way it was
o An initial k means that it sorts by key but maintains the key/value
associations
o A lack of an initial a or k means that it sorts by value but doesn’t
maintain the key/value association (e.g. numerical keys will be
renumbered to reflect the new ordering
o An r before the sort means that the sorting order will be reversed
o An initial u means that a second argument is expected: the name of
a user-defined function that specifies the ordering of any two
elements that are being sorted

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PHP Bible, 2nd
Printing functions forPrinting functions for
arrays (debugging)arrays (debugging)
• bool print_r ( mixed expression [, bool return]) displays information about a
variable in a way that's readable by humans. If given a string, integer or float,
the value itself will be printed. If given an array, values will be presented in a
format that shows keys and elements. Similar notation is used for objects.
print_r() and var_export() will also show protected and private properties of
objects with PHP 5, on the contrary to var_dump().
o Remember that print_r() will move the array pointer to the end. Use reset()
to bring it back to beginning

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PHP Bible, 2nd
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