ECMAScript array.reduce

[danaur]

Hi,

I'm trying to calculate the deviation from an array. Something like

var u_max = []

for(var idx = 0; wait(1) && idx < samples; idx++){
  const frequ = Scope.Channel1.measure("Frequency");
  u_max[idx] = Scope.Channel1.measure("Maximum");
  Scope.wait();
}

const u_max_mean = u_max.reduce((a, b) => a + b, 0) / u_max.length;

But I get a parse exception

Uncaught exception at <anonymous script, id=1898586689712>:48: SyntaxError: Parse error
48 const u_max_mean = u_max.reduce((a, b) => a + b, 0) / u_max.length;

Is array.reduce not available in the WaveForms inbuild scripting engine?

[attila]

Hi @danaur

You can use:
print(u_max.reduce(function(total, num){return total + num;})/u_max.length);

You also have such stats available in the Scope Measurement enabled under the Show menu:

[danaur]

Thanks @attila

print(u_max.reduce(function(total, num){return total + num;}) / u_max.length;

does work like a charm.

I want to calculate the standard deviation and just for the completeness is there a cleaner way than doing a loop?

What works:

    // calculation standard deviation
    var SDprep = 0;
    for(var key in u_max) 
       SDprep += Math.pow((parseFloat(u_max[key]) - u_max_mean),2);
    const u_max_dev = Math.sqrt(SDprep/(u_max.length-1));

This throws a parse exception:

u_max_dev = Math.sqrt(u_max.map(function(x){return Math.pow(x - u_max_mean, 2);}).reduce(function(total, num){return (total + num)/u_max.length;})

I wonder if array.map is the issue here. It's propably a stupid mistake again.

 

Edit:

I know about the inbuild measurement functions. Quite useful.
I couldn't figure out how to access the Scope.Measurements.Frequency Mean value in a script and how to reset the measurements from script.

Edited April 19, 2023 by danaur

[attila]

Hi @danaur

You are missing one parenthesis at the end.
u_max_dev = Math.sqrt(u_max.map(function(x){return Math.pow(x - u_max_mean, 2);}).reduce(function(total, num){return (total + num)/u_max.length;}))

After your first post I've added functions to be able to read mean,median... measurements from Script. It will be available in the next sw version.