How do I output the diffence between values of Array A to Array B in Laravel?

Question

I have an array that plucks values to an array like so:

        /* Pluck just the wattage values to an array */
        $realtime_data_array = $latestrtfeed->nth(60)->reverse()->pluck('data')->toArray();

which results in:

array:150 [▼
  0 => 20277.6
  1 => 20281.4
  2 => 20285.3
  3 => 20289.7
  4 => 20293.8
  5 => 20298.6
  6 => 20303.2
  7 => 20307.4
  8 => 20311.5
  9 => 20315.8
  10 => 20319.8

these value get inputted to the chart like so:

    $realtime_consumption_chart->dataset('kWh', 'line', $realtime_data_array);

The problem is that the sensor is storing cumulative values and I only want to show the difference between value 0 and value 1 then difference between value 1 and value 2 and so on and so on.

How would I go about something like that?

I am going to take a shot and say that I'm going to have to do a FOREACH on the array and create a new array with the values adjusted, but how do I go about that? maybe:

    foreach ($realtime_data_array as $data) {
        $realtime_data_array_corrected = ($data[1]-$data[0])->toArray();
    }

Nope there is something I'm doing wrong or not considering here.

Dusan Radovanovic · Accepted Answer · 2019-03-16 16:29:54Z

1

for ($i = 0; $i < sizeof($realtime_data_array); $i++) {
    if($i==0) {
       $realtime_data_array_corrected[$i] = 0;
       continue;
    }
    $realtime_data_array_corrected[$i] = $realtime_data_array[$i] - $realtime_data_array[$i-1];
}

edited Mar 16, 2019 at 16:29

answered Mar 16, 2019 at 16:10

Dusan Radovanovic

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4 Comments

Frank Barcenas Over a year ago

I get an error of: "Undefined offset: 150" on line" $realtime_data_array_corrected[$i] = $realtime_data_array[$i] - $realtime_data_array[$i-1]; " thank you so much by the way.

Frank Barcenas Over a year ago

Maybe it's not taking into account that there wille be nothing to compare the last value to. If there are 150 value and the first one starts at 0 then the last value will be 149. There will be no 150 I suppose. That might be the issue here.

Dusan Radovanovic Over a year ago

You are right, I edited the code, it should be < instead of <= in loop condition

Dusan Radovanovic Over a year ago

If the code works as expected, you can accept the answer also :D

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