Difference between "as $key => $value" and "as $value" in PHP foreach
PhpArraysForeachPhp Problem Overview
I have a database call and I'm trying to figure out what the $key => $value
does in a foreach
loop.
The reason I ask is because both these codes output the same thing, so I'm trying to understand why it's written this way. Here's the code:
1)In foreach use $key => $value
foreach($featured as $key => $value){
echo $value['name'];
}
this outputs the same as:
2)In foreach use only $value
foreach($featured as $value) {
echo $value['name'];
}
So my question is, what is the difference between $key => $value
or just $value
in the foreach
loop. The array is multidimensional if that makes a difference, I just want to know why to pass $key
to $value
in the foreach
loop.
Php Solutions
Solution 1 - Php
Well, the $key => $value
in the foreach loop refers to the key-value pairs in associative arrays, where the key serves as the index to determine the value instead of a number like 0,1,2,... In PHP, associative arrays look like this:
$featured = array('key1' => 'value1', 'key2' => 'value2', etc.);
In the PHP code: $featured
is the associative array being looped through, and as $key => $value
means that each time the loop runs and selects a key-value pair from the array, it stores the key in the local $key
variable to use inside the loop block and the value in the local $value
variable. So for our example array above, the foreach loop would reach the first key-value pair, and if you specified as $key => $value
, it would store 'key1'
in the $key
variable and 'value1'
in the $value
variable.
Since you don't use the $key
variable inside your loop block, adding it or removing it doesn't change the output of the loop, but it's best to include the key-value pair to show that it's an associative array.
Also note that the as $key => $value
designation is arbitrary. You could replace that with as $foo => $bar
and it would work fine as long as you changed the variable references inside the loop block to the new variables, $foo
and $bar
. But making them $key
and $value
helps to keep track of what they mean.
Solution 2 - Php
Let's say you have an associative array like this:
$a = array(
"one" => 1,
"two" => 2,
"three" => 3,
"seventeen" => array('x'=>123)
);
In the first iteration : $key="one"
and $value=1
.
Sometimes you need this key ,if you want only the value , you can avoid using it.
In the last iteration : $key='seventeen'
and $value = array('x'=>123)
so to get value of the first element in this array
value, you need a key
, x in this case: $value['x'] =123
.
Solution 3 - Php
A very important place where it is REQUIRED to use the key => value
pair in foreach
loop is to be mentioned. Suppose you would want to add a new/sub-element to an existing item (in another key) in the $features
array. You should do the following:
foreach($features as $key => $feature) {
$features[$key]['new_key'] = 'new value';
}
Instead of this:
foreach($features as $feature) {
$feature['new_key'] = 'new value';
}
The big difference here is that, in the first case you are accessing the array's sub-value via the main array itself with a key to the element which is currently being pointed to by the array pointer.
While in the second (which doesn't work for this purpose) you are assigning the sub-value in the array to a temporary variable $feature
which is unset after each loop iteration.
Solution 4 - Php
The difference is that on the
foreach($featured as $key => $value){
echo $value['name'];
}
you are able to manipulate the value of each iteration's $key
from their key-value pair. Like @djiango answered, if you are not manipulating each value's $key
, the result of the loop will be exactly the same as
foreach($featured as $value) {
echo $value['name']
}
Source: You can read it from the PHP Documentation:
>The first form loops over the array given by array_expression. On each iteration, the value >of the current element is assigned to $value and the internal array pointer is advanced by >one (so on the next iteration, you'll be looking at the next element).* > >The second form will additionally assign the current element's key to the $key variable on >each iteration.
If the data you are manipulating is, say, arrays with custom keys, you could print them to screen like so:
$array = ("name" => "Paul", "age" => 23);
foreach($featured as $key => $value){
echo $key . "->" . $value;
}
Should print:
name->Paul
age->23
And you wouldn't be able to do that with a foreach($featured as $value)
with the same ease. So consider the format above a convenient way to manipulate keys when needed.
Cheers
Solution 5 - Php
Say you have an array like this:
$array = (0=>'123',1=>'abc','test'=>'hi there!')
In your foreach loop, each loop would be:
$key = 0, $value = '123'
$key = 1, $value = 'abc'
$key = 'test', $value = 'hi there!'
It's great for those times when you need to know the array key.
Solution 6 - Php
Sample Array: Left ones are the keys, right one are my values
$array = array(
'key-1' => 'value-1',
'key-2' => 'value-2',
'key-3' => 'value-3',
);
Example A: I want only the values of $array
foreach($array as $value) {
echo $value; // Through $value I get first access to 'value-1' then 'value-2' and to 'value-3'
}
Example B: I want each value AND key of $array
foreach($array as $key => $value) {
echo $value; // Through $value I get first access to 'value-1' then 'value-2' and to 'value-3'
echo $key; // Through $key I get access to 'key-1' then 'key-2' and finally 'key-3'
echo $array[$key]; // Accessing the value through $key = Same output as echo $value;
$array[$key] = $value + 1; // Exmaple usage of $key: Change the value by increasing it by 1
}
Solution 7 - Php
if the array looks like:
- $featured["fruit"] = "orange";
- $featured["fruit"] = "banana";
- $featured["vegetable"] = "carrot";
the $key will hold the type (fruit or vegetable) for each array value (orange, banana or carrot)
Solution 8 - Php
here $key will contain the $key associated with $value in $featured. The difference is that now you have that key.
array("thekey"=>array("name"=>"joe"))
here $value is
array("name"=>"joe")
$key is "thekey"
Solution 9 - Php
foreach($details as $key =>$values){
if($values['created_by'] != $user->id && $values['created_by'] != ''){
unset($details[$key]);
}
}