I am using node-red (JS) to take data from a sensor transmitting over MQTT. Sensor data is parsed as an array of 4 values [a, b, c, d] relating to 4 different measurements.

This data is stored into a global array named dataArray, which is a 2 dimensional array.

dataArray[0] = [a, b, c, d];

so that

dataArray[i][0] = Temperature
dataArray[i][1] = VibrationX
dataArray[i][2] = VibrationY
dataArray[i][3] = VibrationZ

The standard way i'd access the contents of this array would be

dataArray[i][j]

However, I get the error "Cannot access property of undefined" when attempting to read the array to calculate averages.

Ok, so i removed the second dimension, and tried accessing dataArray[0] - This returned 'array[0]' an empty array.

Then i attempted to just return the dataArray as passed to the function: i.e.

function average(data)
{
    return data;
}

average(dataArray);

this also returned array[0].

Finally I manaully specified the array within the funtion

dataArray = [[a, b, c, d], [a1, b1, c1, d1]];

and this returned the expected result.

I think it has something to do with the way the array is passed to the definition, or the way that the object is stored in global before access, but no amount of googling has helped me figure this out.

code:

    function Average(data) {
        var temperatureValue = 0;
        var vibXValue = 0;
        var vibYValue = 0;
        var vibZValue = 0;
        for (var i = 0, n = data.length; i < n; i++) {
            temperatureValue = data[i][0] + temperatureValue;
            vibXValue = data[i][1] + vibXValue;
            vibYValue = data[i][2] + vibYValue;
            vibZValue = data[i][3] + vibZValue;
        }
        //Average values from each array element
        var msg1 = [];
        //msg1 = [temperatureValue / n, vibXValue / n, vibYValue / n, vibZValue / n]
    
        //DEBUG - Send dataArray straight through, and it's length
        msg1 = [data, data.length];
        return msg1;
    } 



var dataArray = global.get("dataArray")||[];
var sensorData = msg.payload;

 //This is the input from the Cron node. As long as the input to the function isn't "ClearArray" then push new MQTT messages to the dataArray.
if (msg.payload != "ClearArray") {        
        dataArray.push(sensorData);
}

else if (dataArray.length != 0) {
    msg1 = Average(dataArray);
    msg2 = Peak(dataArray);
    msg.payload = [msg1, msg2];
    //global.set("dataArray",[]);
    return msg;
}