Example R scripts
The open-source statistical package R is able to produce a variety of
fine graphs that can be easily exported into PDF and postscript formats.
This page demonstrates how easily a large variety of graphs can be
generated. (Of course, other tools are also available for
creating graphs -- here is a page that shows how to generate the same
graphs using jgraph.)
Some general things.
This is not a basic introduction to R.
See
In this ``log'' graph
(pdf,
source,
data file 1,
data file 2),
a logarithmic scale is used on the y axis.
Note some of the features on this graph.
- read.table() is used to load data from a text file.
- plot() is used to create axes and labels.
- lines() is used to plot single curves.
- t.test() is used to test if the means of the two data sets differ.
- legend() is used to manually create a legend.
- print() is used to output the graph.
In this multi-line graph
(source,
pdf,
data file),
several lines are plotted from the one data file.
Note some of the features on this graph.
- Subsets of data are chosen.
- A mix of strategies have been used to distinguish sets of
lines from each other.
- Tick marks are manually placed.
In this graph
(source,
pdf,
data file,
data file),
simple R commands are used to filter the data,
and print an average every tenth point instead of printing
every point.
Note some of the features on this graph.
- Two plots are added to the same set of axis.
- R is used to process the data prior to plotting.
A graph with
two axes
(source,
pdf,
data)
is useful for plotting two curves that have the same domain but
different ranges.
- plot() is used to draw plots of the graph with desired
mark type and line style.
- use type ='n' to suppress the drawing of axes, then
- use axis to draw each axis with desired style.
- since the two y-axes are of different ranges, 2 separate plots
are used to draw plots for the 1st and 2nd y-axis.
par(new=TRUE) is used so that the two plots end up in a
single graph.
- Each axis needs major and minor ticks, axis() is called twice to
draw minor and major ticks.
- use 'pos' in y-axis (x-axis) to specify the location of y-axis
(x-axis) relative to x-axis (y-axis).
- use legend() to draw legend manually.
- mtext() is used for drawing the label of the 2nd y-axis.
Text is placed on
this graph (pdf,
source) using the
text function.
The most basic form of the function is
text(x, y, "text")
- This places the word "text" at the point (x, y).
- x, y and text can all be vectors. If vectors of different lengths are used, the shorter vectors are recycled.
Error bars
A graph with
error bars
(source,
pdf,
data 1,
data 2,
data 3,
data 4)
and points.
Note
- Shifting of points to left and right to
separate out the points shown at each integer level.
- Use of a function (with variable number of arguments)
- Use of the arrows() function to draw error bars
Bar graphs
Another useful form of graph is a
bar graph
(pdf,
source,
data).
- A simple bar graph that makes use of the transpose function t()
Tips 'n' tricks
"join"ing two files
f1 <- read.table("data1",col.names=c("word","freq"))
f2 <- read.table("data2",col.names=c("word","length"))
d <- merge(f1,f2,by="word")
d now has three columns word, freq, length
this saves having to use awk as a preprocessor...
Maintained by Andrew Turpin