PHP - Incrementally add array value - php

Question

Basically I have this from a query:
Array
(
[0] => Array
(
[period] => 2014-03
[val] => 2.19
[type] => TypeX
),
[1] => Array
(
[period] => 2014-03
[val] => 2.02
[type] => TypeY
)
)
Using a foreach loop to populate another array we will call DATA, I want the to get the following:
Array
(
[TypeX] => Array
(
[2014-03] => 2.19
)
[TypeY] => Array
(
[2014-03] => 2.02
)
)
The whole thing is looped because my query needs to run each time for a different period. Current exemple, second loop would run for 2014-04. My problem is when I arrive for the 2nd time at my DATA array, I want this:
Array
(
[TypeX] => Array
(
[2014-03] => 2.19
[2014-04] => 1.10
)
[TypeY] => Array
(
[2014-03] => 2.02
[2014-04] => 4.74
)
)
My code is roughly like this:
$data = array();
foreach($graph_period as $period){
$rows = Queryfunction($period,$WHERE,$byType);
foreach($rows as $row){
$data[$row['type']] = array($row['period']=>$row['val']);
}
}
Because the key of the first level (TypeX, TypeY) are the same, the valei is overwritten. How am I to append the array instead of overwriting ?

Answer 1

foreach($rows as $row){
$data[$row['type']][$row['period']] = $row['val']);
}

Answer 2

You only need to change a tiny bit. Inside the foreach where you set the value:
if( !isset($date[$row['type']]) ) {
$data[$row['type']] = array();
}
$data[$row['type']][$row['period']] = $row['val'];
So, you create the array only if it does not exist.