How to dynamically set array keys in php

I have some logic that is being used to sort data but depending on the user input the data is grouped differently. Right now I have five different functions that contain the same logic but different groupings. Is there a way to combine these functions and dynamically set a value that will group properly. Within the function these assignments are happening

For example, sometimes I store the calculations simply by:

$calcs[$meter['UnitType']['name']] = ...


but other times need a more specific grouping:

$calcs[$meter['Resource']['name']][$meter['UnitType']['name']][date('Y-m',$start)] =...


As you can see sometimes it is stored in a multidiminesional array and other times not. I have been trying to use eval() but without success (not sure that is the correct approach). Storing the data in a temporary variable does not really save much because there are many nested loops and if statements so the array would have to be repeated in multiple places.

EDIT

I hope the following example explains my problem better. It is obviously a dumbed down version:

if()
$calcs[$meter['UnitType']['name']] = $data;
else
while ()
$calcs[$meter['UnitType']['name']] = $data;




Now the same logic can be used but for storing it in different keys:

if()
$calcs[$meter['Resource']['name']][$meter['UnitType']['name']][date('Y-m',$start)] = $data;
else
while ()
$calcs[$meter['Resource']['name']][$meter['UnitType']['name']][date('Y-m',$start)] = $data;




Is there a way to abstract out the keys in the $calc array so that I can have one function instead of having multiple functions with different array keys?

6 Answers
6

Would it not be easier to do the following

$calcs = array(
$meter['Resource']['name'] => array(
$meter['UnitType']['name'] => 'Some Value',
$meter['UnitType']['name2'] => 'Some Value Again'
),
);


or you can use Objects

$calcs = new stdClass();
$calcs->$meter['UnitType']['name'] = 'Some Value';


but I would advice you build your structure in arrays and then do!

$calcs = (object)$calcs_array;


or you can loop your first array into a new array!

$new = array();
$d = date('Y-m',$start);
foreach($meter as $key => $value)

$new[$key]['name'][$d] = array();



Give it ago and see how the array structure comes out.

Try to use a switch case.

<?php
$userinput = $calcs[$meter['UnitType']['name']] = $data;;

switch ($userinput)
case "useriput1":
while ()
$calcs[$meter['Resource']['name']][$meter['UnitType']['name']][date('Y-m',$start)] = $data;

break;
case "userinput2":
while ()
$calcs[$meter['Resource']['name']][$meter['UnitType']['name']][date('Y-m',$start)] = $data;

break;

...

default:
while ()
$calcs[$meter['Resource']['name']][$meter['UnitType']['name']][date('Y-m',$start)] = $data;


?>


I agree with the comment on the OP by @Jake N that perhaps using objects is a better approach. Nonetheless, if you want to use arrays, you can check for the existence of keys in a conditional, like so:

if(
array_key_exists('Resource', $meter)
)
$calcs[$meter['Resource']['name']][$meter['UnitType']['name']][date('Y-m',$start)] = $data;
else
$calcs[$meter['UnitType']['name']] = $data;



On the other hand, if you want to use objects, you can create a MeterReading object type, and then add MeterReading instances as array elements to your $calcs array, like so:

MeterReading

MeterReading

$calcs

// Object defintion
class MeterReading
private $data;
private $resource;
private $startDate;
private $unitType;

public function __construct(Array $meter, $start, $data)
$this->unitType = $meter['UnitType']['name'];
$this->resource = $meter['Resource']['name'];
$this->startDate = date('Y-m',$start);


public function data()
return $this->data;


public function resource()
return $this->resource;


public function startDate()
return $this->startDate;


public function unitType()
return $this->unitType;



// Example population
$calcs = new MeterReading($meter, $start, $data);

// Example usage
foreach($calcs as $calc)
if($calc->resource())
echo 'Resource: ' . $calc->resource() . '<br>';

echo 'Unit Type: ' . $calc->unitType() . '<br>';
echo 'Start Date: ' . $calc->startDate() . '<br>';
echo 'Data: ' . $calc->data() . '<br>';



Obviously you can take this further, such as checking the existence of array keys in the object constructor, giving the object property resource a default value if not provided, and so on, but this is a start to an OO approach.

resource

You can use this if you want to get&set array values dynamically.

function getVal($data,$chain)
$level = $data;
for($i=0;$i<count($chain);$i++)
if(isset($level[$chain[$i]]))
$level = $level[$chain[$i]];
else
return null; // key does not exist, return null

return $level;


function setVal(&$data,$chain,$value)
$level = &$data;
for($i=0;$i<count($chain);$i++)
$level = &$level[$chain[$i]]; // set reference (&) in order to change the value of the object

$level = $value;



How it works:

Calling getVal($data,array('foo','bar','2017-08')) will return the equivalent of $data['foo']['bar']['2017-08'].

getVal($data,array('foo','bar','2017-08'))

$data['foo']['bar']['2017-08']

Calling setVal($data,array('foo','bar','2017-08'),'hello') will set value as if you called
$data['foo']['bar']['2017-08'] = 'hello'. non-existent keys will be created automatically by php magic.

setVal($data,array('foo','bar','2017-08'),'hello')

$data['foo']['bar']['2017-08'] = 'hello'

This can be useful if you want to build the structure of the array dynamically.

Here's a function I wrote for setting deeply nested members on arrays or objects:

function dict_set($var, $path, $val)
if(empty($var))
$var = is_array($var) ? array() : new stdClass();

$parts = explode('.', $path);
$ptr =& $var;

if(is_array($parts))
foreach($parts as $part)
if('' == $part)
if(is_array($ptr))
$ptr =& $ptr;

elseif(is_array($ptr))
if(!isset($ptr[$part]))
$ptr[$part] = array();

$ptr =& $ptr[$part];

elseif(is_object($ptr))
if(!isset($ptr->$part))
$ptr->$part = array();

$ptr =& $ptr->$part;



$ptr = $val;

return $var;



Using your example data:

$array = ;

$array = dict_set($array, 'resource1.unit1.2017-10', 'value1');
$array = dict_set($array, 'resource1.unit2.2017-11', 'value2');
$array = dict_set($array, 'resource2.unit1.2017-10', 'value3');

print_r($array);


Results in output like:

Array
(
[resource1] => Array
(
[unit1] => Array
(
[2017-10] => value1
)

[unit2] => Array
(
[2017-11] => value2
)

)

[resource2] => Array
(
[unit1] => Array
(
[2017-10] => value3
)

)

)


The second argument to dict_set() is a $path string in dot-notation. You can build this using dynamic keys with period delimiters between the parts. The function works with arrays and objects.

dict_set()

$path

It can also append incremental members to deeply nested array by using as an element of the $path. For instance: parent.child.child.

$path

parent.child.child.

You can use this library to get or set value in multidimensional array using array of keys:

Arr::getNestedElement($calcs, [
$meter['Resource']['name'],
$meter['UnitType']['name'],
date('Y-m', $start)
]);


to get value or:

Arr::handleNestedElement($calcs, [
$meter['Resource']['name'],
$meter['UnitType']['name'],
date('Y-m', $start)
], $data);


to set $data as value.

$data

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