How to find sum of specific key tags in array

To calculate the values for each date with a specific tag, you can modify the toArray function in your API code as follows:

public function toArray($request)
{
    // Initialize an empty array to hold the results
    $results = [];

    // Loop through each item in the collection
    foreach ($this->collection as $item) {
        // Initialize an empty array to hold the currency totals for this date
        $currencyTotals = [];

        // Loop through each currency for this date
        foreach (unserialize($item->currency) as $currency) {
            // Loop through each key/value pair in the currency array
            foreach ($currency as $key => $value) {
                // If this is the first time we've seen this currency, initialize the total to 0
                if (!isset($currencyTotals[$key])) {
                    $currencyTotals[$key] = 0;
                }

                // Add the value to the total for this currency
                $currencyTotals[$key] += $value;
            }
        }

        // Add the date and currency totals to the results array
        $results[] = [
            'date' => $item->date,
            'currencies' => $currencyTotals,
        ];
    }

    // Return the results
    return $results;
}

This method uses two nested loops to iterate through the collection of items and the currencies for each date, respectively. It initializes an empty array to hold the results and a nested array to hold the currency totals for each date. It then iterates through the currencies for each date and for each currency, it iterates through the key/value pairs and adds the value to the total for that currency. Finally, it adds the date and currency totals to the results array and returns it