如何在PHP中编码计算差异？

Can someone help me how to code the differences of the temperature . For example, in channel one the difference should be 3 . channel two should be 10, channel three should be 2. Also, if I change the temperature to negative. how should I code it ? HELP

<?php
$a1=array(
"channelOne"=>"45",
"channelTwo"=>"100",
"channelThree"=>"20"

);

foreach($a1 as $Name=>$Temperature) {
echo "Channel_Name"."<br>".$Name."<br>"."Actual_Temperature"."<br>".$Temperature."<br>";

}

$a2=array(
"channelOne"=>"48",
"channelTwo"=>"90",
"channelThree"=>"22"
);

foreach($a2 as $Name=>$Temperature_Now) {
echo "Channel_Name"."<br>".$Name."<br>"."Temperature_Now"."<br>".$Temperature_Now."<br>";

}

?>

you can use the array_map function for this

$a1=array(
"channelOne"=>"45",
"channelTwo"=>"100",
"channelThree"=>"20"
);
$a2=array(
"channelOne"=>"48",
"channelTwo"=>"90",
"channelThree"=>"22"
);

$diff = array_map(
    function ($a1, $a2)
    {
        return abs($a1-$a2);
    }, $a1,$a2
);
print_r($diff);

Fiddle:http://phpfiddle.org/main/code/cig-k2n

and you want to keep the keys intact you can use array_walk like this.

$a1=array(
"channelOne"=>"45",
"channelTwo"=>"100",
"channelThree"=>"20"
);
$a2=array(
"channelOne"=>"48",
"channelTwo"=>"90",
"channelThree"=>"22"
);

array_walk($a1,
function (&$v, $k) use ($a1,$a2)
{
    $v = abs($a1[$k]-$a2[$k]);
});
print_r($a1);

Fiddle: http://phpfiddle.org/main/code/njd-qeh

Reference: