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Get started with R

R is a language and environment for statistical computing and graphics, which is similar to S-Plus. It is available as Free Software under the terms of the Free Software Foundation's GNU General Public License. The system runs on Windows, Linux, Mac. You can download it from CRAN R project which has software packages for Unix, Linux, Windows, and Mac.

R is a programming language, and runs a ``command'' in an
interactive manner, known as ``interpretor.''
Each command is requested in a form of ``function'':
For example, it is the function `q()` to quit the program.

> q()

Use it as a calculator. We can execute arithmetic operations at the prompt. For example, can be performed by typing

> 8^4 * 12^3

Computation of factorials and combinations can be done by using the function
`factorial()` and `choose()`.
For example, you can obtain and
by

> factorial(16) > choose(20,8)

Use it with computer graphics.
Here we write a simple code to create a probability frequency plot.
To draw it we need to use it as a special function `prob.hist()` written as follows:

prob.hist = function(x,prob,...){ for(i in 1:length(x)){ polygon(c(x[i]-0.5,x[i]-0.5,x[i]+0.5,x[i]+0.5), c(0,prob[i],prob[i],0),...) } }

The probability mass function of Poisson distribution at `x`
with parameter `lambda` is given by

pmf = dpois(x,lambda)Similarly the cumulative distribution function is obtained by

`ppois(x,lambda)`.

n = 15 lambda = 3 x = 0:n prob = dpois(x,lambda) cbind(x,prob) par(mfrow=c(2,1)) plot(c(-0.5,n+0.5),c(0,max(prob)+0.1),type='n',main='p.m.f',xlab='x',ylab='pmf') prob.hist(x,prob,col='green') t = c(-0.5,x,n+0.5) F = ppois(t,lambda) plot(t,F,type='s',col='red',main='c.d.f') lines(c(-0.5,n+0.5),c(1,1),lty=2,col='red') cdf = ppois(x,lambda) cbind(x,cdf)

Programming Note.
The function `par(mfrow=c(2,1))` set the parameter
`mfrow=c(2,1)`
which splits the multiple graphics to assign 2 figures horizontally
and one vertically.

© TTU Mathematics