Page 47 - Applied Statistics Using SPSS, STATISTICA, MATLAB and R

26 1 Introduction

> x
[1] 1 2 3 4 5 6

The [1] means the first element of x . For instance,

> y <- rnorm(12)
> y
[1] -0.1354 -0.2519 0.5716 0.6845 -1.5148 -0.1190
[7] 0.7328 -1.0274 0.3319 -0.3468 -1.2619 0.7146

st
generates and lists a vector with 12 normally distributed random numbers. The 1
th
and 7 elements are indicated. (The numbers are represented here with four digits
after the decimal point because of page width constraints. In R the representation is
with seven digits.) One could also obtain the previous list by just issuing: >
rnorm(12) . Most R functions also behave as procedures in that way, displaying
lists of values in the R console.
A vector can be filled with strings (delimited with “), as in v <-
c(“Pmax”, T80”, T82”). Now v is a vector containing three strings. The
“
“
second vector element, v[2], is “T80”
R also provides a function, named seq , to define evenly spaced number
sequences, as in the following example:

> seq(-1,1,0.2)
[1] -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

A matrix can be obtained in R by suitably transforming a vector. For instance,

> dim(x) <- c(2,3)
> x
[,1] [,2] [,3]
[1,] 1 3 5
[2,] 2 4 6

transforms (through the dim function) the previous vector x into a matrix of 2×3
elements. Note the display of row and column numbers.
One can also aggregate vectors into a matrix by using the function c bind
(“column binding”) or rbind (“row binding”) as in the following example:

> u <- c(1,2,3)
> v <- c(-1,-2,-3)
> m <- cbind(u,v)
> m
u v
[1,] 1 -1
[2,] 2 -2
[3,] 3 -3

Matrix indexing in R uses square brackets as index qualifier. As an example,
m[2,2] has the value -2 .
Note that R is case-sensitive. For instance, Cbind cannot be used as a
replacement for cbind .