Creating an array of associative arrays in PHP

Question

I am fetching rows from the DB and returning the result in JSON. The output needs to be an array of associative arrays.

$i = 0;
foreach($resultSet as $r)
{
 $output[$i]['key1'] = $r['col1'];
 $output[$i]['key2'] = $r['col2'];
 ...
 $output[$i]['keyN'] = $r['colN'];
 $i++;
}

Is there a more elegant way to do this? Is there anything wrong with this approach? If yes, what is it?

• Corbin: Which DB API are you using? If PDO, your best bet will be to alias the columns to whatever you want their names to be (SELECT a as b or SELECT a b) and then use fetchAll(). Not sure what other APIs have a method like that.

Answer 1

Instead of declaring $i=0; before the loop, you can also write :

foreach($resultSet as $i => $r)
{
 $output[$i]['key1'] = $r['col1'];
 $output[$i]['key2'] = $r['col2'];
 ...
 $output[$i]['keyN'] = $r['colN'];
}

Also, if you could rename your column in the DB query, you could have :

foreach($resultSet as $i => $r)
{
 $output[$i] = $r;
}

Which is pretty much like doing $output = $resultSet;

Edit : If you do need to do some processing on $resultSet for whatever reason and you'd rather have different names, you can consider doing :

for (array('key1' => 'col1', ... 'keyN' => 'colN' as key => col)
{
 $output[$i][$key] = $r[$col];
}

• gentrobot: The $i IS outside the loop in my actual code. I have updated the question. The reason I am not using the resultset directly is that I do some operation on the resultset array before output. But I think, I might as well think about modifying my query and do all the operatrions in the SQL itself, so that I could simply return the resultset. Isn't it ?
• SylvainD: Oops I messed up when I copy-pasted in my editor. You can consider my first comment then.
• SylvainD: I edited my post. Not sure if it would help.

Answer 2

Assuming you are trying to map Columns from the resulting rows such that:

Row | Column 1 | Column 2
1 | Value 1 | Value 2
2 | Value 2 | Value 2

Results in:

$rows = array(
 1 => array(
 'Column 1' => 'Value 1',
 'Column 2' => 'Value 2'
 ),
 2 => array(
 'Column 1' => 'Value 1',
 'Column 2' => 'Value 2'
 ),
);

If your PDO returns the values in numerical position, you can do this:

$columns = array(
 'Column 1',
 'Column 2'
);
$rows = array_map(function($row) use ($columns) {
 return array_combine($columns, $row);
}, $resultSet);

Or, if the $resultSet is associative, and you want to keep the names:

$columns = array_flip(array(
 'Column 1',
 'Column 2'
));
$rows = array_map(function($row) use ($columns) {
 return array_intersect_key($row, $columns);
}, $resultSet);

OR, if your PDO returns them in an Associative array, but the Column names need to be change:

$columns = array(
 'Column 1' => 'Key 1',
 'Column 2' => 'Key 1'
);
$rows = array_map(function($row) use ($columns) {
 $return = array();
 foreach($columns as $from => $to) {
 $return[$to] = !empty($row[$from]) ? $row[$from] : NULL;
 }
 return $return;
}, $resultSet);

That last one would work for either situation, really, as it will take the value at $row[$from] and place it at $result[$to], which would account for numerical indices or string indices. Also, the empty() check will suppress PHP errors, and will ensure that you have a value at each position.

Answer 3

Perhaps something like this?

$i = 0;
foreach($resultSet as $key => $value){
 $output[$i++][$key] = $value;
}

Given a $resultSet like this:

$resultSet['key0'] = 'value0';
$resultSet['key1'] = 'value1';
$resultSet['key2'] = 'value2';
$resultSet['key3'] = 'value3';
$resultSet['key4'] = 'value4';
$resultSet['key5'] = 'value5';

The above code will produce something as follows:

Array (
 [0] => Array ( [key0] => value0 )
 [1] => Array ( [key1] => value1 )
 [2] => Array ( [key2] => value2 )
 [3] => Array ( [key3] => value3 )
 [4] => Array ( [key4] => value4 )
 [5] => Array ( [key5] => value5 )
)

Echoing $output[0]['key0] will output value0 (or an array if value0 is an array).

As a side note, you could actually get completely rid of $i, and just do the following:

foreach($resultSet as $key => $value){
 $output[][$key] = $value;
}

Do let me know if I completely misunderstood the question at hand though :)