Nearest array element by key in reverse order

Question

I have custom code where I get nearest user from array by array key:

$users = [
    "4" => "John",
    "7" => "Alex",
    "13" => "Smith",
    "95" => "Taylor"
];

$id = 9;

$nearestUserByIdInReverseOrder = false;

foreach($users as $userId => $name) {
    if($id >= $userId) {
        $nearestUserByIdInReverseOrder = $name;
    }
}

echo $nearestUserByIdInReverseOrder;

When I change var $id to 3 or smaller number then don't get result. How to get first element of array when $id smaller then it. And can be shorted or optimized code if I've incorrect logic operation in my code? Maybe this possible without looping.

Here is demo

Can you elaborate on what "nearest" mean in your case, and give a few examples? e.g. an `$id` of 12 *or* 14 would yield `Smith` as a result? — Jeto, Aug 31 '20 at 11:55
What do you expect if your `$id` is equally between 2 `$users`? For exampe, say you have users `20` and `22` and `$id` is `21`? — GrumpyCrouton, Aug 31 '20 at 11:56
When current id 12 then result equal to `Alex` and when 14 `Smith`. You can see my demo [code](https://3v4l.org/OelF2) — Andreas Hunter, Aug 31 '20 at 11:58
Downvoted for unclear question (specially because of not mentioning "order" in your expectation). — MLFR2kx, Aug 31 '20 at 12:39

Nick · Accepted Answer · 2020-08-31T12:03:48.220

1

If you want to get the first value in your array if $id is less than any of the array keys, you can initialise $nearestUserByIdInReverseOrder to the first element in the array using reset:

$users = [
    "4" => "John",
    "7" => "Alex",
    "13" => "Smith",
    "95" => "Taylor"
];

$id = 3;

$nearestUserByIdInReverseOrder = reset($users);
foreach($users as $userId => $name) {
    if($id >= $userId) {
        $nearestUserByIdInReverseOrder = $name;
    }
}

echo $nearestUserByIdInReverseOrder;

Output:

John

Demo on 3v4l.org

Note that for this (or your original code) to work, the keys must be in increasing numerical order. If they might not be, ksort the array first:

ksort($users);

edited Aug 31 '20 at 12:03

answered Aug 31 '20 at 11:58

Nick

138,499
22
57
95

But, sir, if you enter ``94`` for an example, the nearest of ``94`` is ``95`` and this will return ``Smith`` instead of ``Taylor``, isn't it? – OMi Shah Aug 31 '20 at 12:03
@OMiShah OP wants the closest name below the `$id` value. See their demo code and also their comment on values to return when `$id=12` or `$id=14`. – Nick Aug 31 '20 at 12:04
Hmm, then it's okay. I had asked to clear my general query, don't mind :) – OMi Shah Aug 31 '20 at 12:06
@OMiShah no problem at all. – Nick Aug 31 '20 at 12:09
This answer also results in `Alex` for `$id = 12` – MLFR2kx Aug 31 '20 at 12:27
@MLF that is what OP wants, see their comments to the question – Nick Aug 31 '20 at 21:52

score 0 · Answer 2 · answered Aug 31 '20 at 12:00

0

Based on your explanation you want to reverse the comparison logic. Also, you want to break out of the loop when you have found the key that is greater, or else you will always get the greatest number:

foreach($users as $userId => $name) {
    if($userId > $id) {
        $nearestUserByIdInReverseOrder = $name;
        break;
    }
}

I have removed the = as that would return 4 for $id = 4 instead of 7. If that is not the desired behavior then add it back.

If the array is not guaranteed to be in ascending order of keys then you need to sort first:

ksort($users);

answered Aug 31 '20 at 12:00

AbraCadaver

78,200
7
66
87

When id 14 result must be `Smith` instead of `Taylor` as your code result. – Andreas Hunter Aug 31 '20 at 12:06
Then your question is unclear _How to get first element of array **when $id smaller then it**._ 14 is not smaller than 13. – AbraCadaver Aug 31 '20 at 12:09
People learn from mistakes usually. If you see my mistake please correct me then. – Andreas Hunter Aug 31 '20 at 12:12
The mistake is that the question is not clear on what you want. What if `$id = 12`? Do you still want `Smith` or do you want `Alex`. – AbraCadaver Aug 31 '20 at 12:14
When 12 result must be `Alex`. Why your not see to my demo code on question and try any number and see to results? – Andreas Hunter Aug 31 '20 at 12:20

score 0 · Answer 3 · answered Aug 31 '20 at 12:14

0

function findClosest($array, $index) {
    ksort($array);
    $idx = array_keys($array)[0];
    foreach ($array as $key => $value) {
        if ($key > $index) return $array[$idx];
        $idx = $key;
    }
}

$users = [
    "13" => "Smith",
    "4" => "John",
    "7" => "Alex",
    "95" => "Taylor"
];

$id = 3;

echo findClosest($users, $id);

answered Aug 31 '20 at 12:14

MLFR2kx

977
7
16

if you pass $id = 12 and run the code, it will return ``Alex`` instead of ``Smith`` – OMi Shah Aug 31 '20 at 12:17
@OMiShah From OP: "_When current id 12 then result equal to `Alex` and when 14 `Smith`._" – GrumpyCrouton Aug 31 '20 at 12:22
@OMiShah That's OK because the greatest index before 12 is 7 and 13 is greater than 12, so it shouldn't return that. That's the basic meaning of "order" in a sorted list. – MLFR2kx Aug 31 '20 at 12:37

Morgosus · Answer 4 · 2020-08-31T12:12:34.093

-1

You could use array_keys() (props to Jeto) on the array, search for the closest number in that (this for reference) and then grab the name based on that.

This would work and the logic is pretty simple, although there may be better solutions. I'm sure someone can use it at some point for something :)

edited Aug 31 '20 at 12:12

answered Aug 31 '20 at 11:57

Morgosus

807
5
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Nearest array element by key in reverse order

4 Answers4