How to get the keys of empty elements in an array if the corresponding element in a similar-sized array is a number (without iteration)?

Question

I have two same-sized arrays $array1 and $array2, both with the usual consecutive numerical keys. $array1 contains numbers, $array2 contains text. I cannot change this structure to accommodate multi-dimensional arrays or what.

Without going through the whole array, how do I get the keys i of the elements in $array2 where

$array1[i] is a number; BUT
$array2[i] is empty?

For example:

// numbers
$array1 = array(NAN, NAN, 1, 0, 3.5, NAN, 2, 4, 0.5);

// text
$array2 = array(FALSE, FALSE, "abc", "abc", FALSE, FALSE, "text", "abc", FALSE);

expected result:

// keys of $array2 where $array1[i] is a number and
// $array2[i] is empty/null/false

Array
(
    [0] => 4
    [1] => 8
)

I've been trying to implement array_keys() and array_udiff() and other PHP array functions to do this but I just can't.

Help, guys, thanks!

Please post some more data. and have you tried this $var as $key => $value — ThinkingMonkey
– ThinkingMonkey, Commented Dec 28, 2011 at 14:51
If you need to check if a value exists for $array2[ i ] you can use the isset directive php.net/manual/en/function.isset.php — Yaniro
– Yaniro, Commented Dec 28, 2011 at 14:54
thanks, @ThinkingMonkey. question updated. any thoughts now? — Ana Ban
– Ana Ban, Commented Dec 28, 2011 at 15:17
"Without going through the whole array". Impossible unless you convert to another datastructure. To convert to another datastructure you have to "go through the whole array", though. — goat
– goat, Commented Dec 28, 2011 at 15:37
thanks, @chris, what's the fastest/most efficient way to do this, then? — Ana Ban
– Ana Ban, Commented Dec 28, 2011 at 15:50

goat · Accepted Answer · 2011-12-28 15:56:32Z

2

This will perform in linear O(n) time.

$keys = array();
foreach ($array1 as $i => $v1) {
    if (is_numeric($v1) && !$array2[$i])
        $keys[] = $i;
}

is_numeric() accepts a little more than what most people consider "numbers", but if that's a problem just replace with another function.

I also assumed your definition of "empty" is a value that php would convert to boolean false. Again, adjust as necessary.

answered Dec 28, 2011 at 15:56

goat

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1 Comment

Ana Ban Over a year ago

lol, was about to update with my similar but less elegant answer. awesome, dude, thanks! and btw, is_numeric() and false are spot on.

Andreu Ramos · Accepted Answer · 2011-12-28 14:53:38Z

0

i'd do something like this:

<?php
    $keys = array();
    foreach($array1 as $iterator){
        $key = array_search($iterator,$array1);
        $elem_in_array1 = $array1[$key]; //= $iterator
        $elem_in_array2 = $array2[$key];
        if(is_numeric($elem_in_array1) && emtpy($elem_in_array2)){
            $keys[] = $key;
        }
    }
?>

answered Dec 28, 2011 at 14:53

Andreu Ramos

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1 Comment

Ana Ban Over a year ago

thanks @Andreu, i'm so sorry, i should've included that i was trying to avoid going through the whole array. but if there's no other way, i'll definitely give this a spin. any thoughts? thanks man

Jonathan Rich · Accepted Answer · 2011-12-28 15:06:36Z

0

This will grab the first value in $arr1 that matches $value, as well as the corresponding value in $arr2 at the index of the value found in $arr1.

<?php

function array_magic ($value, $arr1, $arr2) {
    $index = array_search($value, $arr1);

    if ($index === false) {
        return false;
    }

    if(!isset($arr2[$index])) {
        $value2 = null;
    } else {
        $value2 = $arr2[$index];
    }

    return array( $value, $value2 );
}

answered Dec 28, 2011 at 15:06

Jonathan Rich

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2 Comments

Ana Ban Over a year ago

hi @Jonathan, thanks, i'm sorry i just updated the question: i was trying to avoid going through the whole array. that possible?

Jonathan Rich Over a year ago

I noticed your update and have updated my response in turn. array_search still iterates through the array, but it does so in C so it's faster than a foreach.

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