Best way to test if array key exists - php

Question

Imagine that I want to create an array from another array like this:
$array = array('bla' => $array2['bla'],
'bla2' => $array2['bla2'],
'foo' => $array2['foo'],
'Alternative Bar' => $array['bar'],
'bar' => $array2['bar']);
What is the best way to test either the $array2 has that index I'm passing to the other array, without using an if for each index I want to add.
Note that the key from the $array can be different from the $array2

Answer 1

What I did was, creating a template to the array with the keys that I want e.g.
$template = array('key1', 'key2', 'key3');
Then, I would merge the template with the other array, if any key was missing in the second array, then the value of the key would be null, this way I don't have the problem of warnings telling me about offset values.
$template = array('key1', 'key2', 'key3');
$array = array_merge($template, $otherarray);

Answer 2

if i understood right...
$a = array('foo' => 1, 'bar' => 2, 'baz' => 3);
$keys = array('foo', 'baz', 'quux');
$result = array_intersect_key($a, array_flip($keys));
this will pick only existing keys from $a

Answer 3

A possibility would be:
$array = array(
'bla' => (isset($array2['bla']) ? $array2['bla'] : ''),
'bla2' => (isset($array2['bla2']) ? $array2['bla2'] : ''),
'foo' => (isset($array2['foo']) ? $array2['foo'] : ''),
'xxx' => (isset($array2['yyy']) ? $array2['yyy'] : ''),
'bar' => (isset($array2['bar']) ? $array2['bar'] : '')
);
If this shoud happen more dynamically, I would suggest to use array_intersect_key, like soulmerge posted. But that approach would have the tradeoff that only arrays with the same keys can be used.
Since your keys in the 2 arrays can vary, you could build something half-dynamic using a mapping array to map the keys between the arrays. You have at least to list the keys that are different in your arrays.
//key = key in $a, value = key in $b
$map = array(
'fooBar' => 'bar'
);
$a = array(
'fooBar' => 0,
'bla' => 0,
'xyz' => 0
);
$b = array(
'bla' => 123,
'bar' => 321,
'xyz' => 'somevalue'
);
foreach($a as $k => $v) {
if(isset($map[$k]) && isset($b[$map[$k]])) {
$a[$k] = $b[$map[$k]];
} elseif(isset($b[$k])){
$a[$k] = $b[$k];
}
}
That way you have to only define the different keys in $map.

Answer 4

You want to extract certain keys from array1 and set non-existing keys to the empty string, if I understood you right. Do it this way:
# Added lots of newlines to improve readability
$array2 = array_intersect_key(
array(
'bla' => '',
'bla2' => '',
'foo' => '',
# ...
),
$array1
);

Answer 5

Perhaps this...
$array = array();
foreach ( $array2 as $key=>$val )
{
switch ( $key )
{
case 'bar':
$array['Alternative bar'] = $val;
break;
default:
$array[$key] = $val;
break;
}
}
For any of the "special" array indexes, use a case clause, otherwise just copy the value.