Multiply Two colums in an array and find their sum - php

Question

I have this array structure (see below) grouped by date from a database query, and I wish to find the total for each group by multiplying the quantity by the transamount.
This is what i have so far:
array (size=3)
'2017-7-03' =>
array (size=3)
0 =>
array (size=4)
'paydate' => string '2017-7-03' (length=9)
'tariff' => string 'batch1' (length=31)
'quantity' => string '1.0000' (length=6)
'transamount' => string '20.0000' (length=7)
1 =>
array (size=4)
'paydate' => string '2017-7-03' (length=9)
'tariff' => string 'Eye Test' (length=8)
'quantity' => string '1.0000' (length=6)
'transamount' => string '5.0000' (length=6)
2 =>
array (size=4)
'paydate' => string '2017-7-03' (length=9)
'tariff' => string 'hub photos' (length=16)
'quantity' => string '1.0000' (length=6)
'transamount' => string '82.0000' (length=7)
'2017-7-04' =>
array (size=9)
0 =>
array (size=4)
'paydate' => string '2017-7-04' (length=9)
'tariff' => string ' Register' (length=21)
'quantity' => string '1.0000' (length=6)
'transamount' => string '20.0000' (length=7)
The aim is to get to total of all transaction grouped by the dates.

Answer 1

This may not work since I'm not sure if you need to access the transactions using the date as a key... But something like this would add an element to each array item with the total.
// loop through the arrays sorted by date
foreach ($groups as $group)
{
$total = 0;
// loop through each transaction
foreach ($group as $transaction)
{
// Add to the total for each purchase group
$total += $transaction->quantity * $transaction->transamount;
}
// put the total into the group array
$group->total = $total
}
With this you should end up with something like
'total' => (calculated value),
'2017-7-03' =>
array (size=3)
0 =>
array (size=4)
'paydate' => string '2017-7-03' (length=9)
'tariff' => string 'batch1' (length=31)
'quantity' => string '1.0000' (length=6)
'transamount' => string '20.0000' (length=7)
1 =>
array (size=4)
'paydate' => string '2017-7-03' (length=9)
'tariff' => string 'Eye Test' (length=8)
'quantity' => string '1.0000' (length=6)
'transamount' => string '5.0000' (length=6)
2 =>
array (size=4)
'paydate' => string '2017-7-03' (length=9)
'tariff' => string 'hub photos' (length=16)
'quantity' => string '1.0000' (length=6)
'transamount' => string '82.0000' (length=7)
'2017-7-04' =>