R/interp.R

In sashahafner/biogas: Process Biogas Data and Predict Biogas Production

interp <- function(times, y, time.out, method = 'linear', extrap = FALSE) {

  # Check arguments
  checkArgClassValue(times, c('numeric', 'integer', 'POSIXct', 'POSIXlt', 'POSIXt', 'POSIX', 'difftime'))
  checkArgClassValue(y, c('numeric', 'integer'))
  checkArgClassValue(time.out, c('numeric', 'integer', 'POSIXct', 'POSIXlt', 'POSIXt', 'POSIX'))
  checkArgClassValue(method, c('character'), expected.values = c('linear', 'natural', 'hyman', 'fmm', 'f1'))
  checkArgClassValue(extrap, 'logical')

  #if(extrap & (max(time.out)>max(times) | min(time.out)<min(times))) warning('Some results are extrapolated. Set extrap = FALSE to prevent this.')

  if(method=='linear') {
    y.out <- approx(times, y, xout = time.out, method = 'linear', rule = ifelse(extrap, 2, 1))$y
  } else if(tolower(method) == 'f1') { 
    y.out <- approx(times, y, xout = time.out, method = 'constant', rule = 2, f = 1)$y
  } else { 
    # Or for natural, hyman, or fmm methods (others will return an error)
    y.out <- spline(times, y, xout = time.out, method = method)$y
    # If no extrapolation, delete extrapolated values
    if(!extrap) y.out[time.out<min(times) | time.out>max(times)] <- NA
  }

  # Check for missing values
  if(any(is.na(y.out)) & !extrap) warning(sum(is.na(y.out)), ' NA(s) in calculated values. If you don\'t mind extrapolation, set extrap = TRUE to avoid this.')

  # Add names to output
  if(is.numeric(time.out) | is.integer(time.out)) {
    names(y.out) <- paste0('t', signif(time.out, 3)) 
  } else {
    names(y.out) <- paste0('t', 1:length(time.out)) 
  }

  return(y.out)
}