R/removedips.R

In mengluchu/APMtools: statistical air pollution mapping tools

#' remove dips
#' @param x a vector that the extreme values are to be removed
#' @description  remove time series points that is less than a certain percentage (by default 15%) of the NO2 measured in the previous or the next time stamp
#' @return time series with dips removed
#' @export

removedips = function(x, perce = 0.15) {
    # x = na.approx(x, rule = 2)

    y = as.numeric(x)
    leng = length(x) - 2
    for (i in 1:leng) {
        ## moving window - check distance
        b = i + 2
        c = i + 1  #center, point to check
        if (any(is.na(x[b]), is.na(x[c]), is.na(x[i])))
            next
        mida = x[c] - x[i]
        midc = x[c] - x[b]

        threshold1 = perce * x[i]
        threshold2 = perce * x[b]
        # check threshold
        if (mida < 0 & midc < 0 & x[c] < threshold1 | x[c] < threshold2) {
            y[c] = NA
        }
    }
    return(y)
}