How to calculate two consecutive values in array - php

Question

I am trying to loop through an array and calculate each value with next one. The data is like
[
['rate' => 1000, 'date' => '2017-07-10'],
['rate' => 2000, 'date' => '2017-08-14'],
['rate' => 3000, 'date' => '2017-08-18'],
['rate' => 1000, 'date' => '2017-07-23']
]
I have this [edited, following an example from another question in stackoverflow]:
#foreach ($users as $user)
#if ($user->admin_id == $active_user) // filtering users under this admin
#foreach ($userbillings as $userbilling)
#if($userbilling->user_id == $user->id) // filtering users
<?php
$count = count($userbilling->created_at);
$rates[] = $userbilling->rate;
$diff = 0;
for ($i=0; $i < $count; $i++) {
if (isset($rates[$i + 1])) {
$thisValue = $rates[$i];
$nextValue = $rates[$i + 1];
$diff = $nextValue - $thisValue;
}
}
echo $diff;
?>
#endif
#endforeach
#endif
#endforeach
This gives me result: 1000 2000 3000 1000 3000
What I want to achieve is to subtract first item from second, second item from third, third item from forth and so on, until it reaches to the last item. For last item, I want to keep the whole number.
I understand that I need to use array and loop here, and I have tried different ways for past 2 weeks, but cannot get even close.
Please suggest me how to make it work, or give me a guideline how I should proceed. I have searched plenty of questions here, but could not find anything right for my problem. If there is any, please suggest me the link.

Answer 1

You haven't specified your preferred output but assuming that you want to end up with an array result of the calculations for all pairs, plus the last element as-is, this should get you on the right track.
I would also second a comment above - do not do this sort of logic in a view as it belongs in a controller or somewhere like a service. Keep your views as simple as possible.
Not tested so please do so yourself:
<?php
$periods = [
['rate' => 1000, 'date' => '2017-07-14'],
['rate' => 3000, 'date' => '2017-08-18'],
['rate' => 2000, 'date' => '2017-08-10'],
['rate' => 3000, 'date' => '2017-08-15'],
['rate' => 1000, 'date' => '2017-08-23'],
];
$lastPeriod = count($periods) - 1;
$ratesForPeriods = [];
foreach ($periods as $index => $currentPeriod) {
if ($index === $lastPeriod) {
$ratesForPeriods[] = $currentPeriod; // add the last as-is
} else {
$nextPeriod = $periods[$index + 1];
$currentDate = new DateTime($currentPeriod['date']);
$interval = $currentDate->diff(new DateTime($nextPeriod['date']));
$ratesForPeriods[] = [
'from' => $currentPeriod['date'],
'to' => $nextPeriod['date'],
'rate' => $currentPeriod['rate'],
'days' => $interval->days,
'total' => $interval->days * $currentPeriod['rate'],
];
}
}
print_r($ratesForPeriods);
Yields:
Array
(
[0] => Array
(
[from] => 2017-07-14
[to] => 2017-08-18
[rate] => 1000
[days] => 35
[total] => 35000
)
[1] => Array
(
[from] => 2017-08-18
[to] => 2017-08-10
[rate] => 3000
[days] => 8
[total] => 24000
)
[2] => Array
(
[from] => 2017-08-10
[to] => 2017-08-15
[rate] => 2000
[days] => 5
[total] => 10000
)
[3] => Array
(
[from] => 2017-08-15
[to] => 2017-08-23
[rate] => 3000
[days] => 8
[total] => 24000
)
[4] => Array
(
[rate] => 1000
[date] => 2017-08-23
)
)
Hope this helps :)

Answer 2

Your question is not clear, but here is an example that might help you!
use array_slice() & array_sum()
$array = array( "0"=>1,"1"=>1,"2"=>5,"3"=>1,"4"=>1,"7"=>1,"8"=>3,"9"=>1);
$keys = array_keys($array);
$array = array_values($array);
$newArr = array();
foreach ($array as $key=>$val) {
$newArr[] = array_sum(array_slice($array, 0, $key+1));
}
$newArr = array_combine($keys, $newArr);
print '<pre>';
print_r($newArr);
print '</pre>';
Reference:
array_slice()
array_sum()
array_combine()
array_keys()

Answer 3

You can access the next item in foreach loop like following code :
foreach ($items as $key => $item)
{
echo !empty($items[$key+1]) ? ($items[$key+1]->rate - $item->rate) : $itema->rate;
}