An introduction to R

1
An introduction to R

• Xueli Liu
• STA4502/5507
• October 1, 2007

2
R and statistics
Packaging a crucial infrastructure to
efficiently produce, load and keep consistent
software libraries from (many) different sources
/ authors Statistics most packages deal with
statistics and data analysis State of the art
many statistical researchers provide their
methods as R packages
3
R as a calculator

• log2(32)
• sqrt(2)
• seq(0, 5, length6)
• plot(sin(seq(0, 2pi, length100)))
• q()-quit R session

4
Variables
gt a 49 gt sqrt(a) gt a "The dog ate my
homework" gt sub("dog","cat",a) 1 "The cat ate
my homework gt a (113) gt a 1 FALSE
numeric
character string
logical
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vectors, matrices and arrays

• vector an ordered collection of data of the same
  type
• a c(1,2,3)
• a3
• gt a2
• matrix a rectangular table of data of the same
  type
• b matrix(999, 10,4)
• b

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Branching
if (logical expression) statements else
alternative statements else branch is optional
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Loops
for(i in 110) print(ii) i1 while(ilt10)
print(ii) iisqrt(i)
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Importing and exporting data

• To deal with rectangular tables in the form of
  tab-delimited text files.
• gt x read.delim(filename.txt)
• also read.table, read.csv
• write.table(x, filex.txt, sep\t)
• setwd change directory

9
Getting help
Details about a specific command gt?
t.test help.search(keyword)
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Preparing Computer Output for Printing

• Save command as a script file for later use
• copy-and-paste that portion of the R commands and
  output of interest into an editor of some kind
  Include only those parts that you need
  cut-and-paste as you go along.
• Command we need so far
• ?shapiro.test
• ?wilcox.test
• ?ks.test
• ?rank

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Web sites
Reference card for basic functions
http//cran.r-project.org/doc/contrib/refcard.pdf
Downloading and help search www.r-project.org cr
an.r-project.org http//www.stat.ufl.edu/xueli/st
a6329/sta6329.html