Iterate a PHP array from a specific key - php

Question

I know how to iterate an array in PHP, but I want to iterate an array from a specific key.
Assume that I have a huge array
$my_array = array(
...
...
["adad"] => "value X",
["yy"] => "value Y",
["hkghgk"] => "value Z",
["pp"] => "value ZZ",
...
...
)
I know the key where to start to iterate ("yy"). Now I want to iterate only from this key to another key.
I know that I don't want to do this:
$start_key = "yy";
foreach ($my_array as $key => $v)
{
if ($key == $start_key)
...
}
I was looking for Iterator, but I don't think this is what I need.

Answer 1

Try combining array_search, array_key, and LimitIterator. Using the example from the LimitIterator page and some extra bits:
$fruitsArray = array(
'a' => 'apple',
'b' => 'banana',
'c' => 'cherry',
'd' => 'damson',
'e' => 'elderberry'
);
$startkey = array_search('d', array_keys($fruitsArray));
$fruits = new ArrayIterator($fruitsArray);
foreach (new LimitIterator($fruits, $startkey) as $fruit) {
var_dump($fruit);
}
Starting at position 'd', this outputs:
string(6) "damson" string(10) "elderberry"
There is a limit to this approach in that it won’t loop around the array until the start position again. It will only iterate to the end of an array and then stop. You would have to run another foreach to do the first part of the array, but that can be easily done with the code we already have.
foreach (new LimitIterator($fruits, 0, $startkey-1) as $fruit) {
var_dump($fruit);
}
This starts from the first element, up to the element before the one we searched for.

Answer 2

foreach always resets the array's array pointer. You just can't do that the way you imagine.
You still have a few ways. The foreach way is just skipping everything until you found the key once:
$start_key = "yy";
$started = false;
foreach ($my_array as $key => $v)
{
if ($key == $start_key) {
$started = true;
}
if (!$started) {
continue;
}
// your code
}
You could as well work with the array pointer and use the while (list($key, $v) = each($array)) method:
$start_key = "yy";
reset($array); // reset it to be sure to start at the beginning
while (list($key, $v) = each($array) && $key != $start_key); // set array pointer to $start_key
do {
// your code
} while (list($key, $v) = each($array));
Alternatively, you can just extract the array you want to iterate over like MarkBaker proposed.

Answer 3

Perhaps something like:
foreach(array_slice(
$my_array,
array_search(
$start_key,array_keys($my_array)
),
null,
true) as $key => $v) {}
Demo

Answer 4

You can use array_keys and array_search.
Like this:
$keys = array_keys( $my_array ); // store all of your array indexes in a new array
$position = array_search( "yy" ,$keys ); // search your starting index in the newly created array of indexes
if( $position == false ) exit( "Index doesn't exist" ); // if the starting index doesn't exist the array_search returns false
for( $i = $position; $i < count( $keys ); $i++ ) { // starting from your desired index, this will iterate over the rest of your array
// do your stuff to $my_array[ $keys[ $i ] ] like:
echo $my_array[ $keys[ $i ] ];
}

Answer 5

Try it like this:
$startkey = array_search('yy', array_keys($my_array));
$endkey = array_search('zz', array_keys($my_array));
$my_array2 = array_values($my_array);
for($i = $startkey; $i<=$endkey; $i++)
{
// Access array like this
echo $my_array2[$i];
}

Answer 6

If this pull request makes it through, you will be able to do this quite easily:
if (seek($array, 'yy', SEEK_KEY)) {
while ($data = each($array)) {
// Do stuff
}
}