如何从数组中获取一个数组值？

Question

Hi I have array like this

Array ( 
  [0] => stdClass Object ( 
     [id] => 1930 [value] => 20)

  [1] => stdClass Object (

     [id] => 1931 [value] => 30 ) 

  [2] => stdClass Object ( 

     [id] => 1937 [value] => 30 ) 

  [3] => stdClass Object ( 

     [id] => 1938 [value] => 20 ) 
)

I want to fetch random array from this. The Id which has greater value(%) should be fetched more time (That value is %).

Answer 1

Make a another array and repeat the index of array for the number of times its value is and then fetch the values randomly this would do what you want

The above mentioned array would be

array(0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,)

Answer 2

$arr = Array ( 
  (Object) array (id => 1930, value => 20),
  (Object) array (id => 1931, value => 30),
  (Object) array (id => 1937, value => 30),
  (Object) array (id => 1938, value => 20));

// count sum of all values
$sum = array_reduce($arr, function ($c, $i) { return $c += $i->value; }, 0);
// get random 
$rand = mt_rand(0, $sum);
echo $rand . "  ";
// select 1st item that sum of values >= random value
$new = array_filter($arr, function ($i) use (&$rand) { if($rand > 0 && ($rand -= $i->value) <= 0) return true; else return false; });
// change key to 0
$new = array_values($new);
echo  $new[0]->id;

Answer 3

One way to solve this is to make a list of the cummulative sum of the values in the array, for instance if the values are 3, 1, and 2 the cummulative sums would be 3, 4 and 6. Then when you want to get a random element, you generate a random integer between 1 maximum sum, and then pick the element whose cumulative sum is largest of those whos cumulative sum is smaller than or equal to the random number. In that way, the chanse of any element being picked is proportional to its value.

So here is the setup, creating the cumulative sums:

var $cumsum = array();
var $sum = 0;
foreach($array as $obj) {
    $sum += $obj->value;
    array_push($cumsum, $sum);
}
var $maxsum = end($cumsum);

And here is the function actually picking an element:

function getRandomObject() {
    var $r = random(1, $max);
    if($r < $cumsum[0]) return $array[0];
    for($i = 0; $i < count($cumsum); $i++)
        if($cumsum[$i]) > $r)
            return $array[$i--];
    return $array[$i];
}

Disclaimar: I have not tested this code, so don't expect it to run on a copy paste. Also, whatever code you use you should probably make sure it returns elements with the right probability using a monte carlo method.