R/find_residuals.R

In jrpriceUPS/Math160UPS: Suite of Functions for Math 160 Classes at the University of Puget Sound

#' Find Residuals
#'
#' This function allows you to find and plot the residuals from a linear fit of two datasets.
#' @export
#' @examples
#' > x = c(1,2,3,4,5,6,7)
#' > y = c(2.5,5.1,6.4,8.4,10.8,13.4,15.3)
#' > find_residuals()
#' What is the name of the list with your x variable?
#'   x
#' What is the name of the list with your y variable?
#'   y
#' The best fit line for these data is:
#'   y = 2.12142857142857 x (x) + 0.357142857142856
#'
#'
#' You can find the residuals by saving the model:
#'   model = lm(y~x)
#'
#' and then typing:
#'   resid(model)
#' 1           2           3           4           5           6           7
#' 0.02142857  0.50000000 -0.32142857 -0.44285714 -0.16428571  0.31428571  0.09285714
#'
#'
#' To plot them, you first need to remove all NAs from x and y
#' (beyond the scope of this course), then type:
#'   plot(x,resid(model))

find_residuals <- function(){

  cat("What is the name of the list with your x variable? \n")
  varname1 = readline()
  cat("What is the name of the list with your y variable? \n")
  varname2 = readline()

  if(grepl("$", varname1, fixed=TRUE)){
    names = strsplit(varname1,"\\$")
    frame = get(names[[1]][1])
    x = frame[[names[[1]][2]]]
  } else{
    x = get(varname1)}

  if(grepl("$", varname2, fixed=TRUE)){
    names = strsplit(varname2,"\\$")
    frame = get(names[[1]][1])
    y = frame[[names[[1]][2]]]
  } else{
    y = get(varname2)}


  xnew = x[!is.na(x)&!is.na(y)]
  ynew = y[!is.na(x)&!is.na(y)]
  x = xnew
  y = ynew


  regress = lm(y ~ x)

  intercept = as.numeric(coefficients(regress)[1])
  slope = as.numeric(coefficients(regress)[2])
  cat(paste("The best fit line for these data is:"))
  cat("\n")
  cat(paste(varname2," = ",toString(slope)," x (",varname1,") + ",toString(intercept),sep=""))

  cat("\n")
  cat("\n")
  cat("\n")
  cat(paste("You can find the residuals by saving the model:"))
  cat("\n")
  cat(paste("model = lm(",varname2,"~",varname1,")",sep=""))
  cat("\n")
  cat("\n")





  cat(paste("and then typing:"))
  cat("\n")
  cat(paste("resid(model)\n"))

  print(resid(regress))
  cat("\n")
  cat("\n")
  cat(paste("To plot them, you first need to remove all NAs from",varname1,"and",varname2,"\n(beyond the scope of this course), then type:\n"))
  cat(paste("plot(",varname1,",resid(model))",sep=""))

  plot(x,resid(regress),xlab=varname1,ylab="Residual")
  abline(0,0)


}