Plot mean and standard deviation by category

Question

I'm trying to plot a plot with mean and sd bars by three levels of a factor.

(After two hours of searching on the internet, then checking the Rbook and Rgraphs book I'm still not finding the answer. I think this is because it is a very simple question.)

I have a simple data frame with three columns: my categories, mean, sd.

I would like to do a plot with the mean by category and its sd bars, just like this one (edit: link broken)

My dataframe looks like this

  color     mean.temp      sd        
  black     37.93431      2.267125        
  red       37.01423      1.852052        
  orange    36.61345      1.339032

I'm so sorry for asking this dumb question but I sincerely couldn't find any simple answer to my simple question.

Answer 1

Create a data.frame holding your data:

foo <- data.frame(color=c("black","red","orange"),
    mean.temp=c(37.93431,37.01423,36.61345),
    sd=c(2.267125,1.852052,1.339032))

Now, we first plot the means as dots, making sure that we have enough room horizontally (xlim) and vertically (ylim), suppressing x axis annotation (xaxt="n") and all axis labeling (xlab="", ylab="").

plot(1:3,foo$mean.temp,pch=19,xlab="",ylab="",xaxt="n",xlim=c(0.5,3.5),
    ylim=c(min(foo$mean.temp-foo$sd),max((foo$mean.temp+foo$sd))))

Next, we plot the standard deviations as lines. You could also use three separate lines commands, which may be easier to read. This way, we first collect the data into matrices via rbind(). R will automatically turn these matrices into vectors and recycle them. The NAs are there so we don't join the end of one line to the beginning of the next one. (Try removing the NAs to see what happens.)

lines(rbind(1:3,1:3,NA),rbind(foo$mean.temp-foo$sd,foo$mean.temp+foo$sd,NA))

Finally, annote the x axis:

axis(side=1,at=1:3,labels=foo$color)

Answer 2

With ggplot:

read data:

df=read.table(text=' color mean.temp   sd
1 black 37.93431 2.267125

2 red 37.01423 1.852052

3 orange 36.61345 1.339032',header=TRUE)

plotting:

 ggplot(df, aes(x=color, y=mean.temp)) + 
     geom_errorbar(aes(ymin=mean.temp-sd, ymax=mean.temp+sd), width=.2) +
     geom_line() +
    geom_point()

output