How to extract sequence of numbers from array?

Question

I have a unordered array of numbers:

$ar1 = [101,4,320,1,2,3,45,46];

and i want to extract longest sequence of numbers in that array and put them in second array? I have tried with usort and I get this:

Array(
[0] => 1
[1] => 2
[2] => 3
[3] => 4
[4] => 45
[5] => 46
[6] => 101
[7] => 320
[8] => 321
[9] => 323)

but how to extract just longest sequence (witch in this case is 1,2,3,4) and put in another array?

UPDATE: Here is a code:

function sub($a,$b)
{
if ($a == $b)
{
    return 0;
}
return ($a<$b)? -1:1;
}

$ar1 = ["101","4","320","321","323","1","3","2","45","46"];
$ar2 = [];
usort($ar1,"sub");
print_r($ar1);

so i want to populate $ar2 with longest sequence in array...

My initial thought would be, you are going to have to write some code — RiggsFolly
– RiggsFolly, Commented Mar 17, 2015 at 15:07

n-dru · Accepted Answer · 2015-03-17 15:52:50Z

0

I got it:

$ar1 = [101,4,320,1,2,3,45,46,47];
sort($ar1);
$first = $ar1[0];//assign first (lowest) number
$i=0;
$ar2 = array(); //this array will contain all arrays of consecutive numbers
foreach($ar1 as $v){
    if($v-$first == 1){
        $ar2[$i][] = $v;
    }else{
        $i++;
        $ar2[$i] = array($v); //difference > 1, we set another array
    }
    $first = $v;
}
//now we look for the longest array
$max = 0;
$longest = array();
foreach($ar2 as $k=>$ar){
    $c = count($ar);
    if($c < $max){
        unset($ar2[$k]); //if it is not the longest, we discard it
    }else{
        $max = $c;
        $longest = $ar;
    }
}
echo"<pre>";
print_r($longest);
echo"</pre>";

Yields:

Array ( [0] => 1 [1] => 2 [2] => 3 [3] => 4 )

Copy, paste, run, enjoy!

edited Mar 17, 2015 at 15:52

answered Mar 17, 2015 at 15:43

n-dru

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2 Comments

n-dru Over a year ago

I'm happy then. Will be even happier when you accept my answer :)

n-dru Over a year ago

Thanks, also change the title - it is not extrapolation in mathematic meaning. And change whont to want.

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