R/norm2.R

In tagtools: Work with Data from High-Resolution Biologging Tags

#' Compute the row-wise vector norm
#'
#' This function is used to compute the row-wise vector norm of X if X is a matrix. If X is a vector (row or column), v is the vector norm.
#' @param X A data structure, vector or matrix.
#' @return The row-wise vector-norm of matrix X, i.e., the square-root of the sum of the squares for each row. If X is a vector (row or column), v is the vector norm and norm2() is equivalent to the built-in function norm(). But if X is a matrix e.g., a triaxial accelerometer or magnetometer matrix, norm() gives the overall norm of the matrix whereas norm2() gives the vector norm of each row (i.e., the field strength in the case of a magnetometer matrix).
#' @export
#' @examples
#' sampleMatrix <- matrix(c(0.2, 0.4, -0.7, -0.3, 1.1, 0.1), byrow = TRUE, nrow = 2, ncol = 3)
#' norm2(X = sampleMatrix)
norm2 <- function(X) {
  if (is.list(X)) {
    X0 <- X
    X <- X0$data
  }
  if (is.matrix(X)) {
    sizearray <- dim(X)
    # If X is a vector (row or column), v is the vector norm.
    if (sizearray[1] == 1 | sizearray[2] == 1) {
      v <- sqrt(sum(X^2))
    } else {
      # If X is a matrix, v is the matrix norm.
      v <- sqrt(rowSums(abs(X)^2))
    }
  } else {
    if (is.vector(X) & !is.list(X)) {
      v <- sqrt(sum(X^2))
    }
  }
  return(v)
}