php: check if an array has duplicates

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I'm sure this is an extremely obvious question, and that there's a function that does exactly this, but I can't seem to find it. In PHP, I'd like to know if my array has duplicates in it, as efficiently as possible. I don't want to remove them like array_unique does, and I don't particularly want to run array_unique and compare it to the original array to see if they're the same, as this seems very inefficient. As far as performance is concerned, the "expected condition" is that the array has no duplicates.

I'd just like to be able to do something like

if (no_dupes($array))
    // this deals with arrays without duplicates
else
    // this deals with arrays with duplicates

Is there any obvious function I'm not thinking of?
How to detect duplicate values in PHP array?
has the right title, and is a very similar question, however if you actually read the question, he's looking for array_count_values.

Answers

You can do:

function has_dupes($array) {
    $dupe_array = array();
    foreach ($array as $val) {
        if (++$dupe_array[$val] > 1) {
            return true;
        }
    }
    return false;
}

Wednesday, August 17, 2022

germyrinn-351852ec52e4

You can exploit a lesser known feature of array_keys(), which is used to return the keys of an array as a new array (i.e. without values.)

It accepts an optional second parameter, search, that allows you to stipulate that you wish to have only those keys returned whose value corresponds to your search. So:

$arr = array('one', 'two', 'one', 'three');
$indexes = array_keys($arr, 'one'); //array(0, 2)

Monday, October 31, 2022

anuraj

You can do it through PHP's array_unique function.

This function traverses through your provided array and returns an array with unique values (repeating values will be removed).

Code to return desired string:

$array = array(5,1,2,1,5,7,10);
$new_array = array_unique($array);
echo implode('', $new_array);

Sunday, November 6, 2022

f._leone

If you have an ES2015 environment (as of this writing: io.js, IE11, Chrome, Firefox, WebKit nightly), then the following will work, and will be fast (viz. O(n)):

function hasDuplicates(array) {
    return (new Set(array)).size !== array.length;
}

If you only need string values in the array, the following will work:

function hasDuplicates(array) {
    var valuesSoFar = Object.create(null);
    for (var i = 0; i < array.length; ++i) {
        var value = array[i];
        if (value in valuesSoFar) {
            return true;
        }
        valuesSoFar[value] = true;
    }
    return false;
}

We use a "hash table" valuesSoFar whose keys are the values we've seen in the array so far. We do a lookup using in to see if that value has been spotted already; if so, we bail out of the loop and return true.

If you need a function that works for more than just string values, the following will work, but isn't as performant; it's O(n²) instead of O(n).

function hasDuplicates(array) {
    var valuesSoFar = [];
    for (var i = 0; i < array.length; ++i) {
        var value = array[i];
        if (valuesSoFar.indexOf(value) !== -1) {
            return true;
        }
        valuesSoFar.push(value);
    }
    return false;
}

The difference is simply that we use an array instead of a hash table for valuesSoFar, since JavaScript "hash tables" (i.e. objects) only have string keys. This means we lose the O(1) lookup time of in, instead getting an O(n) lookup time of indexOf.

Wednesday, August 10, 2022

chimp

Use the array_unique function.

Here is an implentation of a multi-dimensional array_unique function.

function super_unique($array)
{
  $result = array_map("unserialize", array_unique(array_map("serialize", $array)));

  foreach ($result as $key => $value)
  {
    if ( is_array($value) )
    {
      $result[$key] = super_unique($value);
    }
  }

  return $result;
}

Not tested, from the comments in the function manual.

Thursday, December 1, 2022

moovon

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