how to calculate the Euclidean norm of a vector in R?

Question

I tried norm, but I think it gives the wrong result. (the norm of c(1, 2, 3) is sqrt(1*1+2*2+3*3), but it returns 6..

Answer 1

If you have a data.frame or a data.table 'DT', and want to compute the Euclidian norm (norm 2) across each row, the apply function can be used.

apply(X = DT, MARGIN = 1, FUN = norm, '2')

Example:

>DT 

        accx       accy       accz
 1: 9.576807 -0.1629486 -0.2587167
 2: 9.576807 -0.1722938 -0.2681506
 3: 9.576807 -0.1634264 -0.2681506
 4: 9.576807 -0.1545590 -0.2681506
 5: 9.576807 -0.1621254 -0.2681506
 6: 9.576807 -0.1723825 -0.2682434
 7: 9.576807 -0.1723825 -0.2728810
 8: 9.576807 -0.1723825 -0.2775187

> apply(X = DT, MARGIN = 1, FUN = norm, '2')
 [1] 9.581687 9.582109 9.581954 9.581807 9.581932 9.582114 9.582245 9.582378