# Set your working directory
# then remove the "#" in front of the setwd line
#setwd("your working directory here")

# Read the data
myData<-read.csv("growth.csv")

# Extract the useful information
mean.gain<-tapply(myData$gain,
           list(myData$supplement,myData$diet),
           mean)
sd.gain<-tapply(myData$gain,
           list(myData$supplement,myData$diet),
           sd)
n.gain<-tapply(myData$gain,
           list(myData$supplement,myData$diet),
           length)

# The main figure
mids<- barplot(mean.gain,beside=T,
       xlab="Feed type",
       ylab="Weight gain",
       ylim=c(0,35),
       col=grey(c(0,0.3,0.6,1)))

# The error bar
arrows(mids,
       mean.gain+sd.gain,
       mids,
       mean.gain-sd.gain,
       angle=90,
       code=3,
       length=0.1)

# The little text at the bottom
text(mids,2,paste(n.gain),col=c("white",rep("black",3)))

# The legend
legend("topright",legend=rownames(mean.gain),fill=grey(c(0,0.3,0.6,1)))