How to get certain values from multidimensional arrays? - php

Question

Here's the data I am working with right now:
$city = [
[
"name" => "Dhaka",
"areas" => ["d1", "d2", "d3"]
],
[
"name" => "Chittagong",
"areas" => ["c1", "c2", "c3"]
],
[
"name" => "Sylhet",
"areas" => ["s1", "s2", "s3"]
],
[
"name" => "Barisal",
"areas" => ["b1", "b2", "b3"]
],
[
"name" => "Khulna",
"areas" => ["k1", "k2", "k3"]
],
[
"name" => "Rajshahi",
"areas" => ["r1", "r2", "r3"]
],
];
I would like to get a list of data associated with only "name" key.
I would also like to show the data associated with "area" key once the user go for the corresponding "name".
It would be helpful if there were any suggestion on how to better store this data for frequent usage in code.

Answer 1

As long as the names are unique you can do this simple trick:
Example 1
$city = [
[
"name" => "Dhaka",
"areas" => ["d1", "d2", "d3"]
],
[
"name" => "Chittagong",
"areas" => ["c1", "c2", "c3"]
],
[
"name" => "Sylhet",
"areas" => ["s1", "s2", "s3"]
],
[
"name" => "Barisal",
"areas" => ["b1", "b2", "b3"]
],
[
"name" => "Khulna",
"areas" => ["k1", "k2", "k3"]
],
[
"name" => "Rajshahi",
"areas" => ["r1", "r2", "r3"]
],
];
$names = array_column($city, null, 'name');
print_r($names);
Output
Array
(
[Dhaka] => Array
(
[name] => Dhaka
[areas] => Array
(
[0] => d1
[1] => d2
[2] => d3
)
)
[Chittagong] => Array
(
[name] => Chittagong
[areas] => Array
(
[0] => c1
[1] => c2
[2] => c3
)
)
[Sylhet] => Array
(
[name] => Sylhet
[areas] => Array
(
[0] => s1
[1] => s2
[2] => s3
)
)
[Barisal] => Array
(
[name] => Barisal
[areas] => Array
(
[0] => b1
[1] => b2
[2] => b3
)
)
[Khulna] => Array
(
[name] => Khulna
[areas] => Array
(
[0] => k1
[1] => k2
[2] => k3
)
)
[Rajshahi] => Array
(
[name] => Rajshahi
[areas] => Array
(
[0] => r1
[1] => r2
[2] => r3
)
)
)
Now you can lookup by name
print_r($city['Chittagong']['areas']); //["c1", "c2", "c3"]
If the names are not guaranteed to be unique, you'll have to build them using foreach, like this:
Example 2
$city = [
[
"name" => "Dhaka",
"areas" => ["d1", "d2", "d3"]
],
[
"name" => "Chittagong",
"areas" => ["c1", "c2", "c3"]
],
[ /*--- ADDED to show duplication ---- */
"name" => "Chittagong",
"areas" => ["x1", "x2", "x3"]
],
[
"name" => "Sylhet",
"areas" => ["s1", "s2", "s3"]
],
[
"name" => "Barisal",
"areas" => ["b1", "b2", "b3"]
],
[
"name" => "Khulna",
"areas" => ["k1", "k2", "k3"]
],
[
"name" => "Rajshahi",
"areas" => ["r1", "r2", "r3"]
],
];
$output = [];
foreach($city as $k=>$v){
$k = $v['name'];
if(!isset($output[$k])) $output[$k] = []; //initialize
$output[$k][] = $v;
}
print_r($output);
Which will give you something like this:
Array
(
[Dhaka] => Array
(
[0] => Array
(
[name] => Dhaka
[areas] => Array
(
[0] => d1
[1] => d2
[2] => d3
)
)
)
[Chittagong] => Array
(
[0] => Array
(
[name] => Chittagong
[areas] => Array
(
[0] => c1
[1] => c2
[2] => c3
)
)
[1] => Array
(
[name] => Chittagong
[areas] => Array
(
[0] => x1
[1] => x2
[2] => x3
)
)
)
[Sylhet] => Array( ... )
As you can see this adds an extra level in to contain the multiple occurrences. Of course you could just combine the area when duplicate (in the foreach). But that is up to you.
Here is a quick example of that (same data as above):
Example 3
$output = [];
foreach($city as $k=>$v){
$k = $v['name'];
if(!isset($output[$k])) $output[$k] = []; //initialize
$output[$k] = array_merge($output[$k], $v['areas']); //merge the areas
}
print_r($output);
Output
Array
(
[Dhaka] => Array
(
[0] => d1
[1] => d2
[2] => d3
)
[Chittagong] => Array
(
[0] => c1
[1] => c2
[2] => c3
[3] => x1
[4] => x2
[5] => x3
)
....
)
If it was me, I would go with the last one, just because of the simplicity it will have working with it later.
PS. if your pulling data out of a Database with PDO, you can use $stmt->fetchAll(PDO::FETCH_GROUP) which will give you something like the second example automatically. The only caveat here is that the name column is the first one selected in the Query, which is the column it will group on.
Cheers.

Answer 2

If you're just trying to loop through the list of cities and get the names you can just use a foreach loop. If you need something beyond this try to define your question a little more.
foreach ($city as $c) {
echo $c["name"];
}