R Notes: Bar plots

Preparation

Import and preprocess data.

library(MASS)
attach(Boston)
data = as.data.frame(na.omit(Boston))
names(data)

##  [1] "crim"    "zn"      "indus"   "chas"    "nox"     "rm"      "age"    
##  [8] "dis"     "rad"     "tax"     "ptratio" "black"   "lstat"   "medv"

smp.idx = sample(1:nrow(data), 5) # sample 5 rows from the raw data set
y1 = data[smp.idx, 3] # column 3 for the sampled rows
y2 = data[smp.idx, 6] # column 6 for the sampled rows
y3 = data[smp.idx, 7] # column 9 for the sampled rows
new.data = rbind(y1, y2, y3)
labels = paste("S", 1:length(y1), sep="")
legends = c("indus", "rm", "rad")

Simple bar plots

Produce a simple bar plot of Ozone.

barplot(y2, ylim=c(0,max(y2)*1.2), offset=0, 
        axis.lty=1, names.arg=labels, ylab="Value")

Produce a bar plot with box.

barplot(y2, ylim=c(0,max(y2)*1.2), offset=0, 
        axis.lty=1, names.arg=labels, ylab="Value")
box()

Stacked and grouped bar plots

Produce a stacked bar plot in terms of sample.

# Add extra space to right of plot area
par(mar=c(5.1, 4.1, 4.1, 5.1), xpd=TRUE)

barplot(new.data, ylim=c(0,max(y1+y2+y3)*1.2), offset=0, 
        axis.lty=1, names.arg=labels, ylab="Value",
        col=terrain.colors(3))

legend("right", inset=c(-0.2,0), legend=legends, 
       fill=terrain.colors(3), box.col="transparent")

Produce a grouped bar plot in terms of sample.

# Add extra space to right of plot area
par(mar=c(5.1, 4.1, 4.1, 5.1), xpd=TRUE)

barplot(new.data, ylim=c(0,max(new.data)*1.2), offset=0, 
        axis.lty=1, names.arg=labels, ylab="Value", 
        col=terrain.colors(3), beside=TRUE)

legend("right", inset=c(-0.2,0), legend=legends, 
       fill=terrain.colors(3), box.col="transparent")

Produce a grouped bar plot in terms of feature.

# Add extra space to right of plot area
par(mar=c(5.1, 4.1, 4.1, 5.1), xpd=TRUE)

barplot(t(new.data), ylim=c(0,max(new.data)*1.2), offset=0, 
        axis.lty=1, names.arg=legends, ylab="Value", 
        col=terrain.colors(length(labels)), beside=TRUE)

legend("right", inset=c(-0.2,0), legend=labels, 
       fill=terrain.colors(length(labels)), box.col="transparent")

Add error bar

# Add extra space to right of plot area
par(mar=c(5.1, 4.1, 4.1, 5.1), xpd=TRUE)

x = barplot(new.data, ylim=c(0,max(new.data)*1.2), offset=0, 
        axis.lty=1, names.arg=labels, ylab="Value", 
        col=terrain.colors(3), beside=TRUE)

legend("right", inset=c(-0.2,0), legend=legends, 
       fill=terrain.colors(3), box.col="transparent")

plot.error = function (x, y, sd, len=1, col="black", horiz=FALSE) {
  len=len*0.05
  if(!horiz){
    arrows(x0=x, y0=y, x1=x, y1=y-sd, col=col, angle=90, length=len)
    arrows(x0=x, y0=y, x1=x, y1=y+sd, col=col, angle=90, length=len)
  }
  else{
    arrows(x0=y, y0=x, x1=y-sd, y1=x, col=col, angle=90, length=len)
    arrows(x0=y, y0=x, x1=y+sd, y1=x, col=col, angle=90, length=len)
  }
}

sd = new.data*0.1

for (i in 1:3) plot.error(x[i,], new.data[i,], sd=sd[i,])