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I came across a kind of a puzzle today during my coding. I wanted to share and get help from you.

I make a query in to the MySql Database and get results as in an array. So I have an output like this:

 $rows=array(n) { // for each n value elements can have different values
    ["val1"] => string(3) "abc"
    ["val2"] => string(3) "def"
    ["val3"] => string(3) "ghi"
    ["val4"] => string(3) "jkl"
}

So let's say n=4 for instance and i need to create unique pairs that same numbers of pair do not occur in the queue.
What I need is as in the example:

n= 1, 2, 3, 4

Pairs I need to get:

1-2, 1-3, 1-4, 2-3, 2-4, 3-4

I need to avoid the pairs like 2-1. 3-1, 4-1, 3-2, 4-2, 4-3 and 1-1, 2-2, 3-3, 4-4.
For Every Pair, I will Check if this pair of arrays are equal.
How can I do that?

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9
  • do you want to end up with... abc-def, abc-ghi, abc-jkl, def-ghi, def-jkl, ghi-jkl..? Commented Nov 15, 2013 at 1:17
  • nope, i just need to get the unique pairs to check if these two arrays have to same values, so i need to get tem paired up once so it does not check it two times. Commented Nov 15, 2013 at 1:22
  • so........ you literally want, given n=4, just this? 1-2, 1-3, 1-4, 2-3, 2-4, 3-4 Commented Nov 15, 2013 at 1:23
  • n can be any number, so i need to create a logic that does this pars without duplicate regardless what is the value of 'n'. Commented Nov 15, 2013 at 1:25
  • right, n can be whatever, but if n is 4, you want just a list of those pairs of numbers? (I'm confused at what you want) Commented Nov 15, 2013 at 1:26

3 Answers 3

Reset to default
1 
<?php

$n = 4;

for($i = 1; $i<=$n; $i++)
    for($x = 1; $x<=$n; $x++)
        if($i != $x && !isset($array[$x][$i]))
            $array[$i][$x] = '';


//echo '<pre>';
//var_dump($array);
//echo '</pre>';
?>

to output use

<?php

for($i = 1; $i<=$n; $i++)
    for($x = 1; $x<=$n; $x++)
        if(isset($array[$i][$x]))
            echo $i.'-'.$x.', ';

?>

which would be:

if $n = 4

1-2, 1-3, 1-4, 2-3, 2-4, 3-4,

if $n = 10

1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 2-3, 2-4, 2-5, 2-6, 2-7, 2-8, 2-9, 2-10, 3-4, 3-5, 3-6, 3-7, 3-8, 3-9, 3-10, 4-5, 4-6, 4-7, 4-8, 4-9, 4-10, 5-6, 5-7, 5-8, 5-9, 5-10, 6-7, 6-8, 6-9, 6-10, 7-8, 7-9, 7-10, 8-9, 8-10, 9-10,

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5 Comments

Thanks for the answer. That works with no problem. i get all the necessary pairs with this and no duplicates. if the value of n is 100 Do you think it would take too long?
@Justin: 1. what if you try? 2. what if you calculate ?
@Justin it shouldn't take long with a 100, I just did it instantaneously... just use the updated answer, as I don't set the array to = 'YES', I only set it to ''
@zerkms i did not understand what you meant, can you explain what you mean? thank you.
@Arian i am positive on your answer.
1

I'm using the array and I just remove the elements once all the pairs have been made, probably there's a better solution using only for's

  $n = 5;
$array = array("abc","def","ghi","jkl","mno");
$r_temp = $array;
$r_result = array();
foreach($array as $r){
    $i = 0;
    while($i < $n-1){
        array_push($r_result,$r_temp[0].$r_temp[$i+1]);
        $i++;
    }
    $n--;
    array_shift($r_temp); //Remove the first element since all the pairs are used
}

print_r($r_result);

Output would be

Array ( [0] => abcdef [1] => abcghi [2] => abcjkl [3] => abcmno [4] => defghi [5] => defjkl [6] => defmno [7] => ghijkl [8] => ghimno [9] => jklmno )
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1 Comment

this is not what i am trying to get. my target is to make pairs of the element identifying numbers.
0

It is an old question, however it looks like a good example of an XY Problem.

First, a direct answer to your question:

$n = 4;
$pairs = [];
for ($i = 1; $i <= $n; ++$i) {
    for ($j = $i+1; $j <= $n; ++$j) {
        $pairs[] = [$i, $j];
    }
}

(You can check it here).

However, if I understand correctly what you were looking for, it is easier to do so directly with and SQL query:

SELECT mycolumn, COUNT(*) AS total FROM mytable GROUP BY mycolumn HAVING total > 1;

This query will return all repeated entries of column mytable.mycolumn and number of appearances.

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