[R] error bars in line plots

[Ott Toomet]

On 6 Oct 2002, Myriam Abramson wrote:

  |Hi!
  |
  |Could you tell me how I can draw a graph with error bars? 
  |Sorry, I don't use R that often and I couldn't find it easily in the
  |documentation. 

There is no errorbars function in the package.  But you may easily construct
your own using segments().  I add my own versions below (actually, why not
put something similar into the base package?).

You may use it as:
plot(x,y)
errorbars(x,y, dy=dy)

The second function is for using with matplot().

Ott

-----------------------

errorbars <- function(x, y, dy=NULL, dx=NULL, ...) {
  if(dy) {
    segments(x, y-dy, x, y+dy, ...)
  }
  if(dx) {
    segments(x-dx, y, x+dx, y, ...)
  }
}


materrorbars <- function(x, y, dy=NULL, dx=NULL,
                         col=par("col"), lty=par("lty")) {
  M <- ncol(y)
  if(is.matrix(x))
    N <- nrow(x)
  else {
    N <- length(x)
    x <- matrix(x, N, M)
  }
  karv <- rep(col, length.out=M)
  joon <- rep(lty, length.out=M)
  if(!is.null(dy)) {
    for(i in seq(M)) {
      segments(x[,i], y[,i]-dy[,i], x[,i], y[,i]+dy[,i],
               col=karv[i], lty=joon[i])
    }
  }
  if(!is.null(dx)) {
    for(i in seq(M)) {
      segments(x[,i]-dx[,i], y[,i], x[,i]+dx[,i], y[,i],
               col=karv[i], lty=joon[i])
    }
  }
}

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