Sometimes we need to put two or more graphs in a single plot. The most common way to create multiple graphs is using the
par() function to set graphical parameters.
R par() function
We can put multiple graphs in a single plot by setting some graphical parameters with the help of
R programming has a lot of graphical parameters which control the way our graphs are displayed.
par() function helps us in setting or inquiring about these parameters. For example, you can look at all the parameters and their value by calling the function without any argument.
 FALSE ... $yaxt  "s" $ylbias  0.2
You will see a long list of parameters and to know what each does you can check the help section
?par. Here we will focus on those which help us in creating subplots.
mfrow can be used to specify the number of subplot we need.
It takes in a vector of form
c(m, n) which divides the given plot into
m*n array of subplots. For example, if we need to plot two graphs side by side, we would have
n=2. Following example illustrates this.
# sample data for max.temp vector max.temp <- c(Sun = 22, Mon = 27, Tue = 26, Wen = 24, Thu = 23, Fri = 26, Sat = 28) # create a new plotting window and set the plotting area into a 1*2 array par(mfrow = c(1, 2)) # plot a bar chart for max.temp barplot(max.temp, main = "Barplot", names.arg = names(max.temp)) # plot a pie chart for max.temp pie(max.temp, main = "Piechart", radius = 1, labels = names(max.temp))
This same phenomenon can be achieved with the graphical parameter
The only difference between the two is that,
mfrow fills in the subplot region row wise while
mfcol fills it column wise.
# extracting Temperature and Ozone data from the airquality dataset Temperature <- airquality$Temp Ozone <- airquality$Ozone # create a new plotting window and set the plotting area into a 2*2 array par(mfrow=c(2,2)) # Plot 1: Histogram for Temperature hist(Temperature) # Plot 2: Horizontal boxplot for Temperature boxplot(Temperature, horizontal=TRUE) # Plot 3: Histogram for Ozone hist(Ozone) # Plot 4: Horizontal boxplot for Ozone boxplot(Ozone, horizontal=TRUE)
Same plot with the change
par(mfcol = c(2, 2)) would look as follows. Note that only the ordering of the subplot is different.
More Precise Control
The graphical parameter
fig lets us control the location of a figure precisely in a plot.
We need to provide the coordinates in a normalized form as
c(x1, x2, y1, y2). For example, the whole plot area would be
c(0, 1, 0, 1) with
(x1, y1) = (0, 0) being the lower-left corner and
(x2, y2) = (1, 1) being the upper-right corner.
Note: we have used parameters
cex to decrease the size of labels and
mai to define margins.
# make labels and margins smaller par(cex=0.7, mai=c(0.1,0.1,0.2,0.1)) Temperature <- airquality$Temp # define area for the histogram par(fig=c(0.1,0.7,0.3,0.9)) hist(Temperature) # define area for the boxplot par(fig=c(0.8,1,0,1), new=TRUE) boxplot(Temperature) # define area for the stripchart par(fig=c(0.1,0.67,0.1,0.25), new=TRUE) stripchart(Temperature, method="jitter")
The numbers assigned to
fig were arrived at with a hit-and-trial method to achieve the best looking plot.