reformat multidimensional array based on value - php

Question

i have an array in below format
$op = Array
(
[0] => Array
(
[0] => Array
(
[contact_id] => 36
[sender_id] => 79
[sendto] => 9192
)
[1] => Array
(
[event_id] => 145
[sender_id] => 9139
[sendto] => 9192
)
)
[1] => Array
(
[0] => Array
(
[event_id] => 145
[sender_id] => 9272
[sendto] => 9290
)
)
[2] => Array
(
[0] => Array
(
[event_id] => 145
[sender_id] => 9138
[sendto] => 9316
)
[1] => Array
(
[event_id] => 145
[sender_id] => 9283
[sendto] => 9316
)
)
)
i want to filter array in a way that resultant array's key should be different sendto values and all sender_id under that sendto shoud come under that array's key
Desired output
Array
(
[9192] => Array
(
[0] =>79
[1] =>9139
)
[9290] =>Array
(
[0]=>9272
)
[9316] =>Array
(
[0] =>9138
[1] =>9283
)
)
although i tried with below code
foreach ($op as $ok=>$ov)
{
if( array_key_exists($ov['sendto'],$mid))
$mid[$ov['sendto']][]=$ok;
else
$mid[$ov['sendto']]=$ok;
}
but this one display notice:Undefined index: sendto
please tell me where i m doing wrong?? i always stuck in such problem

Answer 1

Something like this:
<?php
//Test Array
$op = array(
array(
array(
'contact_id' => 36,
'sender_id' => 79,
'sendto' => 9192
),
array(
'contact_id' => 145,
'sender_id' => 9139,
'sendto' => 9192
)
),
array(
array(
'contact_id' => 145,
'sender_id' => 9272,
'sendto' => 9290
)
),
array(
array(
'contact_id' => 145,
'sender_id' => 9138,
'sendto' => 9316
),
array(
'contact_id' => 145,
'sender_id' => 9283,
'sendto' => 9316
)
),
);
//Switch array format
$new = array();
foreach($op as $element)
{
foreach($element as $entity)
{
if(!isset($new[$entity['sendto']]))
{
$new[$entity['sendto']] = array();
}
$new[$entity['sendto']][] = $entity['sender_id'];
}
}
//Debug the new array.
print_r($new);

Answer 2

Try:
$mid = array();
foreach($op as $tmp_array)
{
foreach($tmp_array as $message)
{
if (!isset($mid[$message['sendto']]))
$mid[$message['sendto']] = array();
$mid[$message['sendto']][] = $message['sender_id'];
}
}

Answer 3

You should go like this:
foreach ($op as $ok=>$ov)
{
if(!array_key_exists('sendto',$mid))
{
$mid[$ov['sendto']] = array();
}
$mid[$ov['sendto']][] = $ov['sender_id'];
}