add to array if it isn't there already

Question

How do I add elements to an array only if they aren't in there already? I have the following:

$a=array();
// organize the array
foreach($array as $k=>$v){
    foreach($v as $key=>$value){
        if($key=='key'){
        $a[]=$value;
        }
    }
}

print_r($a);

// Output

Array
(
[0] => 1
[1] => 2
[2] => 3
[3] => 1
[4] => 2
[5] => 3
[6] => 4
[7] => 5
[8] => 6

)

Instead, I want $a to consist of the unique values. (I know I can use array_unique to get the desired results but I just want to know)

Answer 1

You should use the PHP function in_array (see http://php.net/manual/en/function.in-array.php).

if (!in_array($value, $array))
{
    $array[] = $value; 
}

This is what the documentation says about in_array:

Returns TRUE if needle is found in the array, FALSE otherwise.

Answer 2

You'd have to check each value against in_array:

$a=array();
// organize the array by cusip
foreach($array as $k=>$v){
    foreach($v as $key=>$value){
        if(!in_array($value, $a)){
        $a[]=$value;
        }
    }
}

Answer 3

Since you seem to only have scalar values an PHP’s array is rather a hash map, you could use the value as key to avoid duplicates and associate the $k keys to them to be able to get the original values:

$keys = array();
foreach ($array as $k => $v){
    if (isset($v['key'])) {
        $keys[$value] = $k;
    }
}

Then you just need to iterate it to get the original values:

$unique = array();
foreach ($keys as $key) {
    $unique[] = $array[$key]['key'];
}

This is probably not the most obvious and most comprehensive approach but it is very efficient as it is in O(n).

Using in_array instead like others suggested is probably more intuitive. But you would end up with an algorithm in O(n²) (in_array is in O(n)) that is not applicable. Even pushing all values in the array and using array_unique on it would be better than in_array (array_unique sorts the values in O(n·log n) and then removes successive duplicates).

Answer 4

if (!in_array(...))  
  array_push(..)

Answer 5

Easy to write, but not the most effective one:

$array = array_unique(array_merge($array, $array_to_append));

This one is probably faster:

$array = array_merge($array, array_diff($array_to_append, $array));

Answer 6

if (!in_array($value, $a))
  $a[]=$value;

Answer 7

Try adding as key instead of value:

Adding an entry

function addEntry($entry) {
    $this->entries[$entry] = true;
}

Getting all entries

function getEntries() {
    return array_keys($this->enties);
}

Answer 8

If you're okay with using shorthands in your code (instead of writing explicit if blocks, like some coding standards recommend), you can further simplify Marius Schulz's answer with this one-liner:

in_array ($value, $array) || $array [] = $value;

Answer 9

If you don't care about the ordering of the keys, you could do the following:

$array = YOUR_ARRAY
$unique = array();
foreach ($array as $a) {
    $unique[$a] = $a;
}

Answer 10

Since there are a ton of ways to accomplish the desired results and so many people provided !in_array() as an answer, and the OP already mentions the use of array_unique, I would like to provide a couple alternatives.

Using array_diff (php >= 4.0.1 || 5) you can filter out only the new array values that don't exist. Alternatively you can also compare the keys and values with array_diff_assoc. http://php.net/manual/en/function.array-diff.php

$currentValues = array(1, 2);
$newValues = array(1, 3, 1, 4, 2);
var_dump(array_diff($newValues, $currentValues));

Result:

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

http://ideone.com/SWO3D1

Another method is using array_flip to assign the values as keys and compare them using isset, which will perform much faster than in_array with large datasets. Again this filters out just the new values that do not already exist in the current values.

$currentValues = [1, 2];
$newValues = [1, 3, 1, 4, 2];
$a = array();
$checkValues = array_flip($currentValues);
foreach ($newValues as $v) {
    if (!isset($checkValues[$v])) {
        $a[] = $v;
    }
}

Result:

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

http://ideone.com/cyRyzN

With either method you can then use array_merge to append the unique new values to your current values.

1. http://ideone.com/JCakmR
2. http://ideone.com/bwTz2u

Result:

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

Answer 11

you can try using "in_array":

function insert_value($value, &$_arr) {
    if (!in_array($value, $_arr)) {
        $_arr[] = $value;
    }
}

Answer 12

Taking Gumbo's idea, making the code work:

$array = array('111111','222222','3333333','4444','5555', 
'AAAAAA', 'BBBBBB', 'CCC', 'DDDDDDD', 'EEEEEEEE', 'FFFFFF', 'GGG',
'AAAAAA', 'BBBBBB', 'CCC', 'DDDDDDD', 'EEEEEEEE', 'FFFFFF', 'GGG',
'222222', 
'666666', '777777', 'HHHH');

print_r($array);

$keys= array();
foreach ($array as $k => $v){
    if (isset($v['value'])) {
        $keys[$v] = $k;
    }
}
$unique = array();
foreach ($keys as $key) {
    $unique[] = $array[$key];
}
print "<br><br>";
print_r($unique);

Gives this:

Array
(
    [0] => 111111
    [1] => 222222
    [2] => 3333333
    [3] => 4444
    [4] => 5555
    [5] => AAAAAA
    [6] => BBBBBB
    [7] => CCC
    [8] => DDDDDDD
    [9] => EEEEEEEE
    [10] => FFFFFF
    [11] => GGG
    [12] => AAAAAA
    [13] => BBBBBB
    [14] => CCC
    [15] => DDDDDDD
    [16] => EEEEEEEE
    [17] => FFFFFF
    [18] => GGG
    [19] => 222222
    [20] => 666666
    [21] => 777777
    [22] => HHHH
)

Array
(
    [0] => 111111
    [1] => 222222
    [2] => 3333333
    [3] => 4444
    [4] => 5555
    [5] => AAAAAA
    [6] => BBBBBB
    [7] => CCC
    [8] => DDDDDDD
    [9] => EEEEEEEE
    [10] => FFFFFF
    [11] => GGG
    [12] => 666666
    [13] => 777777
    [14] => HHHH
)

Answer 13

With array_flip() it could look like this:

$flipped = array_flip($opts);
$flipped[$newValue] = 1;
$opts = array_keys($flipped);

With array_unique() - like this:

$opts[] = $newValue;
$opts = array_values(array_unique($opts));

Notice that array_values(...) — you need it if you're exporting array to JavaScript in JSON form. array_unique() alone would simply unset duplicate keys, without rebuilding the remaining elements'. So, after converting to JSON this would produce object, instead of array.

>>> json_encode(array_unique(['a','b','b','c']))
=> "{"0":"a","1":"b","3":"c"}"

>>> json_encode(array_values(array_unique(['a','b','b','c'])))
=> "["a","b","c"]"

Answer 14

Try this code, I got it from here

$input = Array(1,2,3,1,2,3,4,5,6);
$input = array_map("unserialize", array_unique(array_map("serialize", $input)));