Sum up all "amount" fields in a Laravel collection - php

Question

I am trying to get the total amount collected in a month, let's say January.
I am able to retrieve all the created_at fields which were created in the month of January in the $main_data_January variable. The $main_data_January variable contains this type of results.
As you can see, each item has a field called amount.
Problem
I want to retrieve the value of amount field from each item and sum them up. As I'm doing it in the total_earnings_janunary, but this is where I am facing the problem.
By adding both the amounts, the expected result should be 13000, but
the result is 8000. It is only getting only the first value of amount after being in a loop.
$customers = Tag::all();
$total_earnings_janunary = 0;
$query_date = '2017-01-04';
$start_date_janunary = date('Y-01-01', strtotime($query_date));
$end_date_janunary = date('Y-m-t', strtotime($query_date));
foreach ($customers as $customer) {
if (Auth::User()->gym_code == $customer->gym_code ) {
$main_data_janunarys = DB::table('tags')->whereBetween('created_at', [$start_date_janunary,$end_date_janunary])->get();
}
}
for ($i=0; $i <= count($main_data_janunarys); $i++) {
$total_earnings_janunary = $total_earnings_janunary + $main_data_janunarys[$i]->amount;
dd($total_earnings_janunary);
}

Answer 1

Few things to note:
You're querying the Tag model and storing it in $customers. Resulting entities are not customers. Make sure that's intended.
In the first foreach loop, you are overwriting previous value of the $main_data_janunarys over and over. Use break if that's intended.
In the for loop, you are dding early. Move it outside the loop and you'll see your intended results. In the loop exit condition you should be using < instead of <= as you're starting from zero.
To sum up the collection you could just use Collection::sum() method, like: $main_data_janunarys->sum('amount');.

Answer 2

Try this:
$customers = Tag::all();
$total_earnings_janunary = 0;
$query_date = '2017-01-04';
$start_date_janunary = date('Y-01-01', strtotime($query_date));
$end_date_janunary = date('Y-m-t', strtotime($query_date));
foreach ($customers as $customer)
{
if( Auth::User()->gym_code == $customer->gym_code ) {
$main_data_janunarys = DB::table('tags')->whereBetween('created_at', [$start_date_janunary,$end_date_janunary])->get();
}
}
$total_earnings_january = $main_data_januarys->sum('amount');
You can read further about Laravel's Collection here