Plot

Flexible graphics capability is the strengths of R.

• A histogram can be made by typing:

     > x <- rnorm(1000)
     > hist(x)
  

• Scatter plot can be made by

  > x <- 0:10
  > y <- log(x)
  > plot(x,y)
  

  You can add a straight line of y = a + b x by abline(a, b).

  > abline(0.5, 0.2)    # y-intercept = 0.5,  slope = 0.2
  

  You can add more points by:

  > points (x, x * 0.2, pch=4)  # pch is points "character", i.e., symbol to use
  

  You can connect the points by lines:

  > lines (x, y)
  > lines (x, x * 0.2, lty = 2) # lty is line type
  

  You can see the pre-set points characters:

  > example(points)
  

• To save this plot to a postscript file called, graph1.ps, type

  > dev.print(postscript,file="graph1.ps") 
  > dev.print(pdf,file="graph1.pdf")   # to make pdf
  

  The file, graph1.ps, is saved in the directory in which R is invoked. Other graphical devices (i.e. pdf, jpeg, xfig, etc.) can be specified. To see other graphical devices, see help(Devices).

• A matrix of scatterplots
  

  pairs(X) produces a pairwise scatterplot matrix of the variables defined by the columns of X. Every column of X is plotted against every other column of X.

  > iris[1:5,]   # Anderson's iris data set
  > pairs(iris[1:4], main = "Anderson's Iris Data -- 3 species", 
  +       pch = 21, bg = c("red", "green3", "blue")[unclass(iris$Species)])
  > help(iris)
  > help(pairs)  # Try the examples.
  

• multiple plots per page

  > par(mfrow = c(2,2))
  > for (i in 1:4) { hist(iris[,i], xlab=names(iris)[i], main=i)}
  > par(mfrow=c(1,1))     # setting the parameter back to the default
  

  par(mfcol=c(2,2)) is similar, but figures are filled by column.

• Bar plots:

  > VADeaths                        # death rates per 1000 in Virginian in 1940
  > tVADeaths <- t(VADeaths)[,5:1]  # transpose, and change order of columns
  > mp <- barplot(tVADeaths, beside=T, legend=colnames(VADeaths), ylim=c(0,130))
  > fakeSE <- 2 * sqrt (1000 * tVADeaths/100)  # making a fake error bar
  > mp                              # contains x-coordinates
  > segments (mp, tVADeaths, mp, tVADeaths+fakeSE, lwd=1.5)
  

  You can easily make a customized ``wrapper'' function to do all of this if you repeatedly use the same plotting procedure.

• Advanced graphics:
  See R Graph Gallery for more advanced graphics. The web page contains the example codes to produce the fancy figures, so you can learn through immitation.