PHP Arrays

I was looking for a function that searched an array for another array, and after not finding one I decided to write it. What I was looking for was a function that took a smaller array and searched for that exact sequence of items in a larger array. As it happens, PHP does have a number of array search functions, but they didn't produce the correct result.

The array_search() function does accept an array as the needle to be searched for, but this does a multi-dimensional search instead. I also saw some techniques using array_intersect() or array_diff(), and although these functions were able to find one array inside another I was interested in the sequence.

I came across this sorting algorithm the other day called 'bogo sort'. This is a sort of joke sorting algorithm that is highly ineffective at actually sorting arrays. The name comes from the word 'bogus'.

Here is how it works.

1. Take an array.
2. Shuffle it.
3. If the array sorted then stop.
4. If the array is not sorted then return to step 2.

As you can see, this isn't so much a sorting algorithm, more of a game of chance. Due to the random nature of the sort you might need to wait a very long time before the array is actually sorted.

Here is an implementation of a bogo sort in PHP.

I have been doing some reading and watching lectures of programming theory recently and I was reminded of this algorithm I learned about in university. Binary searching an array is a divide and conquer algorithm that takes an array and searches for a value in that array by splitting the array into halves.

Getting the first or last item from an array in PHP is usually quite easy. If you create an array and then add a bunch of values to it then the array index will increment by 1 for every element you add. This means that in order to get the first element from an array you just reference the default starting position (0). To get the last item in the array the index key will be the length of the array, minus 1. Here is some example code showing this.

<?php
$array = array();
$array[] = 1;
$array[] = 2;

// get the first item in the array
print $array[0]; // prints 1

// get the last item in the array
print $array[count($array) - 1]; // prints 2

Things become slightly more complicated when the array has non standard key values. Take the following array for example in which the array count it started at 1.

A simple way to convert a string into a set of variables is through the use of the explode() and list() functions. list() is a language construct (not really a function) that will convert an array into a list of variables. For example, to convert a simple array into a set of variables do the following:

list($variable1, $variable2) = array(1, 2);

In this example $variable1 now contains the value 1 and $variable2 contains the value 2. This can be adapted to use the explode() function to take a string and convert it into a set of variables. An example of this in use might be when dealing with addresses, simply explode the string using the comma and you have a set of variables.

$address = '123 Fake Street, Town, City, PO3T C0D3';
list($street, $town, $city, $postcode) = explode(',', $address);

You can now print out parts of the address like this:

I have previously talked about Removing commas from the end of strings, but it is also possible to use the implode() function to do the same sort of thing.

implode() takes two parameters, the separator and the array, and returns a string with each array item separated with the separator. The following example shows how this function works.

$array = array(1,2,3,4,5,6);
$list = implode(',', $array);

The $list variable will now contain the string "1,2,3,4,5,6". However, things tend to become messy again when you have an array with empty items in it.

Converting an array of information into a string is easy, but when you are doing this for insertion into a database having trailing commas is going to mess up your SQL statements.

Take the following example, which takes an array of values and converts them into a string of values. This practice is quite common in PHP database manipulation.

$values = array('one', 'two', 'three', 'four', 'five');
$string = '';
 
foreach ( $values as $val ) {
    $string .= '"'.$val.'", ';
}
 
echo $string; // prints "one", "two", "three", "four", "five",

Obviously we need to strip the trailing comma from the end of this string. To do this you can use the following function.

Use the following function to remove all duplicate values in an array.

function remove_duplicated_values($array){
 $newArray = array();
 foreach($array as $key=>$val){
  $newArray[$val] = 1;
 }
 return array_keys($newArray);
}

The way this function works is by looping through the array and assigning each value of the array to be a key of a new array and setting the value as 1. As the values of the array are added to the new array any new values will lengthen the array and any duplicate values will reset to be 1.

The keys of the new array are then returned as an array of values using the array_keys() PHP function.

Here is an example of the function in action.

If you have an object or array that you want to save until a later you can use the serialize() and unserialize() functions. The operation of the functions are straightforward. To serialize() an array just pass the serialise function the array like this.

$array = array(1,2,3,4);
$serializedArray = serialize($array);

Now when we print the serialized array out we get the following.

a:4:{i:0;i:1;i:1;i:2;i:2;i:3;i:3;i:4;}

This contains all of the data needed to recreate our array. Be careful not to edit this string because it will not work if you want to unserialize it and get the array back. You can store this string in a file or a database so that you can recreate the exact same array at a later date.

The array_flip() function in PHP is used to swap the values of an array with the keys. Take the following array.

$array = array('key1'=>'value1', 'key2'=>'value2');

To exchange all the values with the keys we pass it through the array_flip() function.

$array = array_flip($array);
echo '<pre>'.print_r($array, true).'</pre>';

This prints out the following:

Array
(
 [value1] => key1
 [value2] => key2
)

If any of the values are the same then the highest key is overwritten. The following array:

$array = array('a', 'a', 'a', 'b');

Will produce the following array when passed through array_flip().