PHP: Hash Table

What is PHP Hash Table

PHP array, also function as a list of key value pairs. (aka hash-table, dictionary, associative list)

Creating a Hash Table

array(key1 => value1, key2 => value2, etc)

<?php
$x = array("aa" => 19, "bb" => 16);
print_r($x);
# Array ( [aa] => 19 [bb] => 16 )
?>

Get Values

To get value of a element, use the form $arr[key]

<?php
$x = array("aa" => 19, "bb" => 16);
echo($x["aa"]);
# 19
?>

Note that the key should be quoted.

Add A Entry or Modify

$arr[key] = val

If the key exist, old value is replaced. Otherwise, a new entry is added.

<?php
$x = array("aa" => 1, "bb" => 2);
$x["aa"]=18;
print_r($x);
# Array ( [aa] => 18 [bb] => 2 )
?>

Delete a Entry

To delete a entry, use unset()

<?php
$x = array("aa" => 1, "bb" => 2);
unset($x["aa"]);
print_r($x);
# Array ( [bb] => 2 )
?>

Key Exists

To check if a key exists, use array_key_exists

<?php
$x = array("aa" => 2, "bb" => 9);
echo array_key_exists("bb",$x);
# 1
?>

Get Just Keys

To get just the keys, use array_keys()

<?php
$x = array("aa" => 9, "bb" => 6);
print_r(array_keys($x));
# Array ( [0] => aa [1] => bb )
?>

Get Just Values

To get just the values, use array_values(). The function array_values() effectively replaces all the keys by numerical indexes starting from 0.

<?php
$x = array("aa" => 19, "bb" => 16);
print_r(array_values($x));
# Array ( [0] => 19 [1] => 16 )
?>