The solution depends on the PHP version you are using. At least there are 2 solutions:
First [Newer PHP versions]
As @JosepAlsina said before the best and also shortest solution is to use array_column as following:
$catIds = array_column[$objects, 'id'];
Notice: For iterating an array containing \stdClasses as used in the question it is only possible with PHP versions >= 7.0. But when using an array containing arrays you can do the same since PHP >= 5.5.
Second [Older PHP versions]
@Greg said in older PHP versions it is possible to do following:
$catIds = array_map[create_function['$o', 'return $o->id;'], $objects];
But beware: In newer PHP versions >= 5.3.0 it is better to use Closures, like followed:
$catIds = array_map[function[$o] { return $o->id; }, $objects];
The difference
First solution creates a new function and puts it into your RAM. The garbage collector does not delete the already created and already called function instance out of memory for some reason. And that regardless of the fact, that the created function instance can never be called again, because we have no pointer for it. And the next time when this code is called, the same function will be created again. This behavior slowly fills your memory...
Both examples with memory output to compare them:
BAD
while [true]
{
$objects = array_map[create_function['$o', 'return $o->id;'], $objects];
echo memory_get_usage[] . "\n";
sleep[1];
}
// the output
4235616
4236600
4237560
4238520
...
GOOD
while [true]
{
$objects = array_map[function[$o] { return $o->id; }, $objects];
echo memory_get_usage[] . "\n";
sleep[1];
}
// the output
4235136
4235168
4235168
4235168
...
This may also be discussed here
Memory leak?! Is Garbage Collector doing right when using 'create_function' within 'array_map'?
[PHP 5 >= 5.5.0, PHP 7, PHP 8]
array_column — Return the values from a single column in the input array
Description
array_column[array $array, int|string|null $column_key,
int|string|null $index_key = null]: array
Parameters
arrayA multi-dimensional array or an array of objects from which to pull a column of values from. If an array of objects is provided, then public properties can be directly pulled. In order for protected or private properties to be pulled, the class must implement both the __get[] and __isset[] magic methods.
column_key The column of values to return. This value may be an integer key of the column you wish to retrieve, or it may be a string key name for an associative array or property name. It may also be null to return complete arrays or objects [this is useful together with index_key to reindex the array].
index_key
The column to use as the index/keys for the returned array. This value may be the integer key of the column, or it may be the string key name. The value is cast as usual for array keys [however, prior to PHP 8.0.0, objects supporting conversion to string were also allowed].
Return Values
Returns an array of values representing a single column from the input array.
Changelog
| 8.0.0 | Objects in columns indicated by index_key parameter will no longer be cast to string and will now throw a TypeError instead.
|
Examples
Example #1 Get the column of first names from a recordset
The above example will output:
Array
[
[0] => John
[1] => Sally
[2] => Jane
[3] => Peter
]
Example #2 Get the column of last names from a recordset, indexed by the "id" column
The above example will output:
Array
[
[2135] => Doe
[3245] => Smith
[5342] => Jones
[5623] => Doe
]
Example #3 Get the column of usernames from the public "username" property of an object
The above example will output:
Array
[
[0] => user 1
[1] => user 2
[2] => user 3
]
Example #4 Get the column of names from the private "name" property of an object using the magic __get[] method.
The above example will output:
Array
[
[0] => Fred
[1] => Jane
[2] => John
]
If __isset[] is not provided, then an empty array will be returned.
mohanrajnr at gmail dot com ¶
7 years ago
if array_column does not exist the below solution will work.
if[!function_exists["array_column"]]
{
function array_column[$array,$column_name]
{
return array_map[function[$element] use[$column_name]{return $element[$column_name];}, $array];
}
}
WARrior ¶
9 years ago
You can also use array_map fucntion if you haven't array_column[].
example:
$a = array[
array[
'id' => 2135,
'first_name' => 'John',
'last_name' => 'Doe',
],
array[
'id' => 3245,
'first_name' => 'Sally',
'last_name' => 'Smith',
]
];
array_column[$a, 'last_name'];
becomes
array_map[function[$element]{return $element['last_name'];}, $a];
balbuf ¶
4 years ago
This function does not preserve the original keys of the array [when not providing an index_key].
You can work around that like so:
ff2 AT hotmail DOT co DOT uk ¶
4 years ago
Because the function was not available in my version of PHP, I wrote my own version and extended it a little based on my needs.
When you give an $indexkey value of -1 it preserves the associated array key values.
EXAMPLE:
$sample = array[
'test1' => array[
'val1' = 10,
'val2' = 100
],
'test2' => array[
'val1' = 20,
'val2' = 200
],
'test3' => array[
'val1' = 30,
'val2' = 300
]
];
print_r[array_column_ext[$sample,'val1']];
OUTPUT:
Array
[
[0] => 10
[1] => 20
[2] => 30
]
print_r[array_column_ext[$sample,'val1',-1]];
OUTPUT:
Array
[
['test1'] => 10
['test2'] => 20
['test3'] => 30
]
print_r[array_column_ext[$sample,'val1','val2']];
OUTPUT:
Array
[
[100] => 10
[200] => 20
[300] => 30
]
yangmeishu at live dot com ¶
2 years ago
Please note that if you use array_column to reset the index, when the index value is null, there will be different results in different PHP versions, examples