PHP：如何检查数组中最接近给定数字的项？

Question

I need to check which item in an array array( 300, 600, 900, 1200 ) is closest to the number I have stored in a variable $number .

I've looked through the PHP manual for either an approach or a function which will do this for me but my research has found nothing. Hoping someone can suggest something.

Answer 1

If the numbers in the array are always sorted in ascending order, you can loop through once checking distance as you go and soon as you start moving away from your number, return the last good number. Something like this:

<?php
$number = mt_rand(1, 1200);
$array = array(300, 600, 900, 1200);

function closest($number, $array){
    //infinite distance to start
    $dist = INF;
    //remember our last value
    $last = false;

    foreach($array as $v){
        //get our current distance
        $dist2 = abs($number - $v);

        //check if we are getting further than last number was
        if($dist2 > $dist){
            //return our last value
            return $last;
        }
        //set our new distance
        $dist = $dist2;
        //set our last value for next iteration
        $last = $v;
    }
    return $last;
}

echo "<pre>";
var_dump($number);
var_dump(closest($number, $array));

Will output:

Input: int(522)
Output: int(600)

Demo: http://codepad.viper-7.com/NjcdP0

If the values are not sorted, you will need to loop over each value to get a distance and then find the smallest distance. Something like:

<?php
$number = mt_rand(1, 1200);
$array = array(300, 600, 900, 1200);

function closest($number, $array){
    //find distances to number
    $dist = array_map(
        function($val) use ($number) {
            return abs($number - $val);
        },
        $array);
    //flip array so distance is key
    $dist = array_flip($dist);
    //sort distance by key
    ksort($dist);

    //get key for shortest distance
    $key = array_values($dist)[0];

    return $array[$key];
}

echo "<pre>";
echo "Input: ";
var_dump($number);
echo "Output: ";
var_dump(closest($number, $array));

Outputs:

Input: int(677)
Output: int(600)

Demo: http://codepad.viper-7.com/N5nv0v

Answer 2

I'm sure this is not the fastest way to do this, but it can be written simply using usort . After you sort the array by absolute difference from the target number, the closest value will be the first one:

usort($your_array, function($a, $b) use ($number) {
    if ($a == $b) { return 0; }
    return abs($number - $a) > abs($number - $b) ? 1 : -1;
});

$closest = reset($your_array);

---

In PHP 7, the usort callback can be simplified with the combined comparison operator.

usort($your_array, function($a, $b) use ($number) {
    return abs($number - $a) <=> abs($number - $b);
});

Answer 3

You must iterate through and store both current result and difference, like this:

function closest_number(array $array, $number) {
    $result     = null;
    $difference = null;

    foreach ($array as $element) {    
        if ($difference === null || abs($element - $number) < $difference) {
            $difference = abs($element - $number);
            $result     = $element;
        }
    }

    return $result;
}

Answer 4

Here some magic code:

$arr = [300, 600, 900, 1200];
$number = 920;
$deltas = array_reduce(
    $arr, 
    function($t, $v) use ($number) { 
        $t[$v] = abs($v - $number); 
        return $t; 
    },
    []
);
asort($deltas);
echo array_keys($deltas)[0];