R/iv_oneday.R

In etzkorn/postuR: Posture Classification and Activity Measures for Triaxial Accelerometers in ECG Patches.

#' @title Intra-Daily Variability
#'
#' @description Calculate Intra-Daily Variability (IV) from one day of data using
#' a given number of epochs (usually minutes) per bin.
#' @param activity_oneday vector representing timeseries for one day of activity data.
#' Each entry corresponds to one epoch.
#' @param bin_epochs number of epochs per bin to collapse activity_oneday into before performing
#' IV formula.

iv_oneday <- function(activity_oneday, bin_epochs){
    if(length(activity_oneday)%%bin_epochs != 0){
        stop("Variability bin duration must be factor of length(activity_oneday)")
    }

    activity_oneday %*% kronecker(
        diag(length(activity_oneday)/bin_epochs),
        matrix(1/bin_epochs, nrow = bin_epochs, ncol = 1)
    )

    mean.activity = mean(activity_oneday)
    numerator = sum(diff(activity_oneday)^2)/(length(activity_oneday)-1)
    denominator = sum((activity_oneday - mean.activity)^2) / length(activity_oneday)
    return(numerator/denominator)
}