R/best_fit_fct.r

In ManuelLamothe/RapidACi: Automated Rapid A-Ci curve correction for Li-Cor system

#' best_fit function
#'
#' @description Internal function to retrieve coefficients of a fitting polynomial on
#'   empty chamber measurements
#'
#' @param data Data points to regress
#' @param max_degree Inherited argument from Rapid_aci_correction function
#'
#' @return A vector of coefficients of the best fitted curve


best_fit <- function(data, max_degree) {

  if(max_degree%%1 != 0 | max_degree < 1 | max_degree > 5) {
    stop("max_degree only takes integer values from 1 up to 5")
  }

  x  <- lm(GasEx_A ~ Meas_CO2_r, data)
  y  <- lm(GasEx_A ~ poly(Meas_CO2_r, 2, raw = TRUE), data)
  z1 <- lm(GasEx_A ~ poly(Meas_CO2_r, 3, raw = TRUE), data)
  z2 <- lm(GasEx_A ~ poly(Meas_CO2_r, 4, raw = TRUE), data)
  z3 <- lm(GasEx_A ~ poly(Meas_CO2_r, 5, raw = TRUE), data)

  bic <- c(BIC(x), BIC(y), BIC(z1), BIC(z2), BIC(z3))
  bic <- bic[1:max_degree]

  if(which.min(bic) == 1) return(coef(x))
  if(which.min(bic) == 2) return(coef(y))
  if(which.min(bic) == 3) return(coef(z1))
  if(which.min(bic) == 4) return(coef(z2))
  if(which.min(bic) == 5) return(coef(z3))

}