PHP从数组获取相同值的范围

Question

Is there any way to get the key range of same values and make a new array?

Let's say we have an Array Like this in php :

$first_array = ['1'=>'a','2'=>'a','3'=>'a','4'=>'b','5'=>'b','6'=>'a','7'=>'a'];

How can i get this array? Is there any function for this?

$second_array = ['1-3'=>'a','4-5'=>'b','6-7'=>'a'];

Answer 1

Loop through it, extract the keys, generate the ranges and insert to the new array -

$first_array = ['1'=>'a','2'=>'a','3'=>'a','4'=>'b','5'=>'b'];

$flip = array();
foreach($first_array as $key => $val) {
  $flip[$val][] = $key;
}

$second_array = [];
foreach($flip as $key => $value) {
    $newKey = array_shift($value).' - '.end($value);
    $second_array[$newKey] = $key;
}

Output

array(2) {
  ["1 - 3"]=>
  string(1) "a"
  ["4 - 5"]=>
  string(1) "b"
}

Answer 2

regarding your first question you can get range of each value using foreach() loop.

$first_array = ['1'=>'a','2'=>'a','3'=>'a','4'=>'b','5'=>'b'];

foreach($first_array as $key=>$value)
{
        //do your coding here, $key is the index of the array and $value is the value at that range, you can use that index and value to perform array manipulations
}

Regarding your second question it not exactly clear what are trying to implement there. But what ever you want to do like creating a new array with modified index and other things can be done within this foreach() loop itself

I hope this helps you.

Answer 3

If someone is still looking for an answer, here is what I did. Given the array

$first_array = ['0'=>'a',
                '1'=>'a',
                '2'=>'a',
                '3'=>'a',
                '4'=>'a',
                '5'=>'b',
                '6'=>'b',
                '7'=>'a',
                '8'=>'a']

I build a multidimensional array, in which each element is an array of three more elements:

[0] - The value in the first array
[1] - The key where the value starts repeating
[2] - The last key where the value stops repeating

The code

$arrayRange = [];

for($i = 0; $i < count($first_array); $i++){

    if(count($arrayRange) == 0){
        // The multidimensional array is still empty
        $arrayRange[0] = array($first_array[$i], $i, $i);
    }else{
        if($first_array[$i] == $arrayRange[count($arrayRange)-1][0]){
            // It's still the same value, I update the value of the last key
            $arrayRange[count($arrayRange)-1][2] = $i;
        }else{
            // It's a new value, I insert a new array
            $arrayRange[count($arrayRange)] = array($first_array[$i], $i, $i);
        }
    }
}

This way you get a multidimensional array like this:

$arrayRange[0] = array['a', 0, 4]; 
$arrayRange[1] = array['b', 5, 6];
$arrayRange[2] = array['a', 7, 8];