Question

I have a data set, and I would like to apply an equation to groups of my values. Specifically I would like to apply

sqrt(X^2+Y^2+Z^2)

to all values within a specific time and variable

Looking at the data below I would like to group my values by unique time (TS) and Bins (Bin), and grab the square root of the sum of squares for each of the X Y and Z components.

    id  D      Bin  value   Month Day Year Hour Minute Second                  TS
    1   X       V1   -0.320     1  30 2012   13     59     50 2012-01-30 13:59:50
    1   Y       V1   -0.088     1  30 2012   13     59     50 2012-01-30 13:59:50
    1   Z       V1    0.171     1  30 2012   13     59     50 2012-01-30 13:59:50
    1   X       V2    0.368     1  30 2012   13     59     50 2012-01-30 13:59:50
    1   Y       V2   -0.104     1  30 2012   13     59     50 2012-01-30 13:59:50
    1   Z       V2    0.008     1  30 2012   13     59     50 2012-01-30 13:59:50
    2   X       V1   -0.052     1  30 2012   14      0     50 2012-01-30 14:00:50
    2   Y       V1    0.278     1  30 2012   14      0     50 2012-01-30 14:00:50
    2   Z       V1   -0.086     1  30 2012   14      0     50 2012-01-30 14:00:50
    2   X       V2   -0.214     1  30 2012   14      0     50 2012-01-30 14:00:50
    2   Y       V2    0.118     1  30 2012   14      0     50 2012-01-30 14:00:50
    2   Z       V2   -0.030     1  30 2012   14      0                        

So up first would be V1 at 13:59:50

sqrt(-0.320^2 + -0.088^2 + 0.171^2)

and then for V2 at t13:59:50

sqrt(0.368^2 +-0.104^2  + 0,008^2)

and so on

I had tried to use this formula (Data is called “V”)

 V=aggregate(value~TS+variable,data=V,sqrt((if(V$D=="X")V$value^2)+(if(V$D=="Y")V$value^2))+(if(V$D=="Z")V$value^2))

But obviously that does not work. So does anyone have a better way to first index unique groups in a data set, and than apply an equation to said group?

Answer 1

Assuming you always have one X, one Y, and one Z for each combination of (TS, Bin), I would try this:

aggregate(value ~ TS + Bin, data = V, FUN = function(x)sqrt(sum(x^2)))