Find peaks in a vector

peaks.R

#' Find peaks in a vector
#'
#' Which elements of a vector are greater than the value to their left and
#' right? First and last values need only be greater than their adjacent value.
#'
#' @param x vector of values
#' @return boolean vector of peak positions
is_peak <- function(x) {
  n <- length(x)
  x_i_minus_1 <- c(-Inf, x[1:(n - 1)])
  x_i_plus_1 <- c(x[2:n], -Inf)
  (x > x_i_minus_1) & (x > x_i_plus_1)
}

x <- c(3, 2, 1, 2, 4, 0, 1)
peaks <- is_peak(x)
print(x[peaks])