Convert flat array representing a key path into a nested array terminating at an empty array [duplicate]

Try This:

$array = array('apple','orange','tomato');
$count = count($array) - 1;
$tempArray = array();
for($i = $count; $i >= 0; $i--)
{
    $tempArray = array($array[$i] => $tempArray);
}

try it with:

$target = array();
$value = array();
$path = array('apple', 'orange', 'tomato');

$rv = &$target;
foreach($path as $pk)
{
    $rv = &$rv[$pk];
}
$rv = $value;
unset($rv);

print_r($target);

output:

Array
(
    [apple] => Array
        (
            [orange] => Array
                (
                    [tomato] => Array
                        (
                        )

                )

        )

)

Update 1: Explaination

Here I am using reference/variable alias to traverse the dynamic stack of keys. The reference makes it possible to use a stack instead of recursion which is generally more lean. Additionally this code prevents to overwrite existing elements in the $target array. For more detail on references have a look at Reference Explained

$target = array(); //target array where we will store required out put
$value = array(); //last value i.e. blank array
$path = array('apple', 'orange', 'tomato'); //current array

$rv = &$target; //assign address of $target to $rv (reference variable)

foreach($path as $pk)
{
    $rv = &$rv[$pk]; // Unused reference [ex. $rv['apple'] then $rv['apple']['orange'] .. so on ] - actually assigned to $target by reference

    print_r($target);
    echo '-----------------<br />';
}
$rv = $value; //here $rv have unused refernce of value tomato so finally assigned a blank array to key tomoto
//
unset($rv); // Array copy is now unaffected by above reference

echo "final array<br />";
print_r($target);

output:

Array
(
    [apple] => 
)
-----------------
Array
(
    [apple] => Array
        (
            [orange] => 
        )

)
-----------------
Array
(
    [apple] => Array
        (
            [orange] => Array
                (
                    [tomato] => 
                )

        )

)
-----------------
final array
Array
(
    [apple] => Array
        (
            [orange] => Array
                (
                    [tomato] => Array
                        (
                        )

                )

        )

)

In output of explaination you can trace the value of $target in foreach loop

You can try this way also with foreach and ksort:

<?php

$fruits = array(

  "Apple",
  "Orange",
  "Tomato",
  "Banana",
  "Papaya"

);
krsort($fruits);
$tmp = array();
foreach($fruits as $fruit){
        $tmp =  array($fruit => $tmp);
}
echo "<pre>".print_r($tmp, true)."</pre>";

?>

[Proof of concept]

Array
(
    [Apple] => Array
        (
            [Orange] => Array
                (
                    [Tomato] => Array
                        (
                            [Banana] => Array
                                (
                                    [Papaya] => Array
                                        (
                                        )

                                )

                        )

                )

        )

)

While loop and array_pop:

$fruits = [
    "Apple",
    "Orange",
    "Tomato",
    "Banana",
    "Papaya"
];

$output = [];
while ( $fruit = array_pop($fruits) )
{
    $output = [$fruit => $output];
}

$result = array_reduce(array_reverse($fruits), function (array $acc, $fruit) {
    return [$fruit => $acc];
}, []);

You simply start from the inside out and wrap the value into a $key => $value array.