PHP: Get next/prev element of an array with loop if last/first [duplicate]

Question

I don't manage to add a navigation arrow to my portfolio. I would like to get next and prev id based on current id. The issue is when the $current_id is the last of array, I don't know how to go to the first one to create a kind of loop. And the same if the $current_id is the first element, how to have the last element as prev ? I'm stuck, can you please help me ?

Here is my code:

<?php 

    $current_id = "10";

    $array = array(
        "1" => "aa",
        "2" => "bb",
        "3" => "cc",
        "4" => "dd",
        "5" => "ee",
        "6" => "ff",
        "7" => "gg",
        "8" => "hh",
        "9" => "ii",
        "10" => "jj",
    );


    $current_index = array_search($current_id, $array);

    $next = $current_index + 1;
    $prev = $current_index - 1;

?>

Are you sure that your key for array will be remain same like 1,2,3... — Sunil Pachlangia
– Sunil Pachlangia, Commented Sep 22, 2015 at 12:05

Niki van Stein · Accepted Answer · 2015-09-22 12:08:17Z

3

You can use modulo % for that for the next value:

$number_of_elements = count($array);
$next = ($current_index + 1) % $number_of_elements;

And an if for the prev value, since modulo does not like negative numbers

$prev = $current_index - 1
if ($prev < 0){
    $prev = $number_of_elements - 1;
}

edited Sep 22, 2015 at 12:08

answered Sep 22, 2015 at 12:04

Niki van Stein

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Comments

Amarnasan · Accepted Answer · 2015-09-22 12:17:44Z

1

Use modulo THIS way:

$current_id = 9;

$array = array(
    "aa",
    "bb",
    "cc",
    "dd",
    "ee",
    "ff",
    "gg",
    "hh",
    "ii",
     "jj",
);

$next = ($current_id+($count=count($array))+1)%$count;
$previous = ($current_id+$count-1)%$count;

print("$previous $next");

edited Sep 22, 2015 at 12:17

answered Sep 22, 2015 at 12:08

Amarnasan

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1 Comment

Amarnasan Over a year ago

@BasvanStein: It is way more elegant than your solution and the efficiency difference must be close to 1/infinite. Anyway, check it now, you'll find it hyper-efficient.

Jinksy · Accepted Answer · 2015-09-22 12:23:48Z

0

You could use reset() and end() functions to move the array pointer to the beginning and the end of the array. So, before processing your array you could do something like:

end($array);
$end = key($array);

and then:

reset ($array);
while (current ($array)) {
    $current_index = key($array);
    $current_value = current($array);
    if ($current_index == $end) 
        reset($array);
    else
        next($array);
}

Or, build some sort of linked list where every element of your array would have a pointer/reference to the next element.

edited Sep 22, 2015 at 12:23

answered Sep 22, 2015 at 12:08

Jinksy

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Comments

Rohit Kumar · Accepted Answer · 2015-09-22 12:27:02Z

0

You could achieve it , if you have last id of page .

Try something as

$last=count($array);
$next = $current_index + 1;
$next=$next<0?$last:$next;
$prev = $current_index - 1;
$prev =$prev==$last?1:$prev

answered Sep 22, 2015 at 12:27

Rohit Kumar

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