Move specific array items to beginning of array without altering order of the rest

Question

I have an array:

Array
(
    [product1] => Array
    (
        [id] => 1
        [title] => 'p1'
        [extra] => Array(
            [date] => '1990-02-04 16:40:26'
        )
    )

    [product2] => Array
    (
        [id] => 2
        [title] => 'p2'
        [extra] => Array(
            [date] => '1980-01-04 16:40:26'
        )
    )
    [product3] => Array
    (
        [id] => 3
        [title] => 'p3'
        [extra] => Array(
            [date] => '2000-01-04 16:40:26'
        )
    )
    [product4] => Array
    (
        [id] => 4
        [title] => 'p4'
        [extra] => Array(
            [date] => '1995-01-04 16:40:26'
        )
    )
    [product5] => Array
    (
        [id] => 5
        [title] => 'p5'
        [extra] => Array(
            [date] => '1960-01-04 16:40:26'
        )
    )
    ...

I need to get 2 products with the latest date and move them to the start of the array.

I've looked into the multisort function, and I could sort the array like this, but then the entire array would be arranged by date, I want to maintain the order of the array but just bump up the latest 2 rows.

I need to pick out the 2 latest (order by date) from the array, then move these to the start of the array. So the order of the ids should be:

3,4,1,2,5

The latest 2 have been moved to the front of the array, the remainder are still ordered by id.

Could you please provide some more information on what you're trying to achieve? — YaBCK, Jun 05 '15 at 10:51
@panthro Its really unclear what you want to achieve can you post your expected output — Narendrasingh Sisodia, Jun 05 '15 at 10:53
The given array is impossible (duplicate keys), a real array sample would help. — deceze, Jun 05 '15 at 10:55
Suggestion: use a two pass approach. Pick out a unique id of the items that you can use; worst case that's the array keys. Pass over the array once to filter out the two latest items; a `foreach` or `array_reduce` will do. Then do a [stable sort](http://stackoverflow.com/a/17365409/476), using the found ids as comparison criterion (if id == found id, always smaller, else equal). — deceze, Jun 05 '15 at 10:59
I cannot give a var dump, I have simplified the data as the var dump would be huge. — panthro, Jun 05 '15 at 10:59
Alternative: pass over the array to find the keys of the latest items (`foreach` or `array_reduce`), then `array_splice` and `array_merge` it back to together. — deceze, Jun 05 '15 at 11:02

deceze · Answer 1 · 2015-06-05T12:15:11.480

Not the most optimal implementation, but the most straight forward:

$array = /* your data */;

$latest = $array;
uasort($latest, function (array $a, array $b) {
    return strtotime($a['extra']['date']) - strtotime($b['extra']['date']);
});
array_splice($latest, 2);

$latestOnTop = array_merge($latest, array_diff_key($array, $latest));

The array_splice operation requires that your array keys are actually product1 or similar; won't work with numeric indices, as they'll be renumbered. Use another truncation mechanism if that's the case.

If your array is really big, a complete sort will be unnecessarily slow. In that case, you should rather loop over the array once, keeping track of the two latest items (and their keys) you could find, then array_diff_key and array_merge on that. That's a bit more difficult to implement (left as exercise for the reader), but much more efficient.

splash58 · Answer 2 · 2015-06-05T11:37:32.117

// Making array with only dates
$dates = array();
foreach ($arr as $key => $item) 
    $dates[$key] = $item['extra']['date'];
// Sort it by date saving keys
uasort($dates, function($i1, $i2) { return  strtotime($i1) - strtotime($i2); });
// Take keys
$dates = array_keys($dates);
// Create array with two needed items
$newarray = array( $dates[0] => $arr[$dates[0]], $dates[1] => $arr[$dates[1]]);
// remove these items
unset($arr[$dates[0]]);  unset($arr[$dates[1]]); 
// put them in array start
$arr = array_merge($newarray, $arr);
var_dump($arr);

score 0 · Answer 3 · answered Jun 05 '15 at 11:51

// copy current array for new array
$temp = $input; 

// sort temp array by latest date
uasort($temp, function($a,$b) {
    return (strtotime($a['extra']['date']) < strtotime($b['extra']['date']));
});

// for 2 key value pairs to get on top
$sorted_keys = array_keys($temp);

// initialize your required array
$final = [];

// two keys to move on top
$final [ $sorted_keys[0] ] = $temp [ $sorted_keys[0] ];
$final [ $sorted_keys[1] ] = $temp [ $sorted_keys[1] ];

foreach ($input as $k => $v)
{
    // insert your other array values except two latest
    if(!array_key_exists($k, $final))
    {
        $final[$k]=$v;
    }
}

unset($temp); // free up resource

$final is your required array

Move specific array items to beginning of array without altering order of the rest

3 Answers3