使用相同的键组合索引数组

I am using the Flot jQuery plugin to create a graph on how many visitors there have been per platform. I would like to create a 4th line with total visitors, calculated by previously retrieved data.

I need to combine several multi-dimensional Indexed arrays, but not simply merging them recursively. I.E:

$arr1 = [[2016/05/04,2],[2016/05/03,4],[2016/05/02,6]];
$arr2 = [[2016/05/04,1],[2016/05/03,3],[2016/05/02,2]];
$arr3 = [[2016/05/04,6],[2016/05/03,7],[2016/05/02,8]];

The output should be:

$arrTotal = [[2016/05/04,9],[2016/05/03,14],[2016/05/02,16]];

How do I accomplish this in a (fairly) simple way?

First of all, you cannot declare your dates the way you did:

$arr1 = [[2016/05/04,2],[2016/05/03,4],[2016/05/02,6]];

Because it's going to take 2016, divide it by 5 then divide it by 4. You need to put them into quotes.

$arr1 = [['2016/05/04',2],['2016/05/03',4],['2016/05/02',6]];

But to create an associative array, you should do it this way:

$arr1 = array('2016/05/04' => 2, '2016/05/03' => 4, '2016/05/02' => 6);
$arr2 = array('2016/05/04' => 1, '2016/05/03' => 3, '2016/05/02' => 2);
$arr3 = array('2016/05/04' => 6, '2016/05/03' => 7, '2016/05/02' => 8);

Now all you want to do, is loop through each array and sum them up.

$merge = array();

function mergeArray(Array &$merge, Array $array){
    // Loop through each key and value
    foreach($array as $key => $value)
        // Make sure the value is numeric
        if(is_numeric($value)){
            if(!isset($merge[$key]))
                $merge[$key] = $value;
            else
                $merge[$key] += $value;
        }
}

mergeArray($merge, $arr1);
mergeArray($merge, $arr2);
mergeArray($merge, $arr3);

And now if you dump the $merge:

array(3) {
    ["2016/05/04"]=>
        int(9)
    ["2016/05/03"]=>
        int(14)
    ["2016/05/02"]=>
        int(16)
}

Build a method that will sum the values by respecting the keys of existing values.

$arr1 = array('2016/05/04'=>2,'2016/05/03'=>4,'2016/05/02'=>6);
$arr2 = array('2016/05/04'=>1,'2016/05/03'=>3,'2016/05/02'=>2);
$arr3 = array('2016/05/04'=>2,'2016/05/03'=>7,'2016/05/02'=>8);

function array_sum(&$new_arr,$arr) {
    foreach ($arr as $date_key => $num_value) {
        // initialize date in new array with 0, if not done previously
        if (! isset($new_arr[$date_key])) { $new_arr[$date_key] = 0; }

        // add number for indexed element of array
        $new_arr[$date_key] += $num_value;
    }
}

$new_arr = array();
array_sum($new_array,$arr1);
array_sum($new_array,$arr2);
array_sum($new_array,$arr3);

You are trying to sum up every second value from each nested array relatively to their position in the parent array.
There's a short and simple solution using array_map, array_sum and array_column functions:

$groupped = array_map(null, $arr1,$arr2,$arr3);
$result = array_map(function($v){    
    return [$v[0][0], array_sum(array_column($v, 1))];
}, $groupped);

print_r($result);

The output:

Array
(
    [0] => Array
        (
            [0] => 2016/05/04
            [1] => 9
        )

    [1] => Array
        (
            [0] => 2016/05/03
            [1] => 14
        )

    [2] => Array
        (
            [0] => 2016/05/02
            [1] => 16
        )
)