Array merge if key not exists - php

Question

I tried merging two arrays if the key is not exists in the array but I cannot accomplish this. How can i do? This is what I have tried:
array (size=3) // name of the array $exchange
'purchase' => string '1' (length=1)
'agriculture' => string '1' (length=1)
array (size=6) // name of the array $fixed
'purchase' => string '0' (length=1)
'ICT' => string '0' (length=1)
'agriculture' => string '0' (length=1)
'entertainment' => string '0' (length=1)
'goods and service' => string '0' (length=1)
'other' => string '0' (length=1)
foreach($fixed as $keys=>$values){
if(!in_array($values, $exchange, true)){
array_push($exchange, $keys);
}
}
I get this result:
array (size=7)
'ICT' => string '1' (length=1)
0 => string 'purchase' (length=8)
1 => string 'ICT' (length=3)
2 => string 'agriculture' (length=11)
3 => string 'entertainment' (length=13)
4 => string 'goods and service' (length=17)
5 => string 'other' (length=5)
But I want:
array (size=7)
'ICT' => string '1' (length=1)
'purchase' => string '0' (length=8)
'agriculture' => string '0' (length=11)
'entertainment' => string '0' (length=13)
'goods and service' => string '0' (length=17)
'other' => string '0' (length=5)

Answer 1

Try this:
foreach ($fixed as $keys => $values) {
if (! array_key_exists($keys, $exchange)) {
$exchange[$keys] = $values;
}
}
It checks if the key $keys does not already exists in $exchange and adds it together with its value ($values).
Or you can simply replace the entire foreach() block with:
$exchange = $exchange + $fixed;
The addition $exchange + $fixed adds to $exchange the keys (and their values) that are in $fixed but are not in $exchange. The combined array is then stored in $exchange.
Read also this answer. It explains where your code is wrong.

Answer 2

There's a couple of problems with this:
in_array will search the values of the given array, not the keys, so in this case you just end up checking if the value "0" exists in the array $variable. I assume instead you wanted to check if the key already exists.
array_push pushes a new value into the next available key.
What you need is to check if a key exists, and if not, add it with the existing value. Try this instead:
for($fixed as $key=>$value)
{
if(!isset($exchange[$key])) // Check if the key exists
{
$exchange[$key] = $value; // Add the new key -> value pair.
}
}

Answer 3

Try with array_merge (http://php.net/manual/es/function.array-merge.php)
$result = array_merge($array1, $array2);

Answer 4

You can do it in several ways depending the result you desire:
foreach($fixed as $key=>$values){
if(!isset($exchange[$key])){
$exchange[$key]=values;
}
}
or
$exchange += $fixed;
or
$exchange = array_merge($fixed,$exchange);