Togaware DATA MINING
Desktop Survival Guide
by Graham Williams
Google


Vectors

The most basic data structure is a simple vector, a list-like data structure that stores values which are all of the same data type or class. You can either directly create a vector using the R function c (for combine), or else have R create a random list of numbers for you, using, for example runif (which will generate a sequence of random numbers uniformly distributed between the supplied limits).



[basicstyle=\ttfamily\tiny]
> v <- c(1, 2, 3, 4, 5)
> v
[1] 1 2 3 4 5
> class(v)
[1] "numeric"
> v <- runif(20, 0, 100)
> v
 [1] 69.717291 98.491863 98.541503 72.558488 85.607629 35.441444 59.622427
 [8] 40.191194  8.311273 24.215177 77.378846 55.563735 71.554547 97.522348
[15]  2.186403 52.528335 69.281037 44.634309  2.063750 47.125579

The vector function will create a vector of a specific mode (logical, by default):

> vector(length=10)
 [1] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
> vector(mode="numeric", length=10)
 [1] 0 0 0 0 0 0 0 0 0 0

Various sequences of numbers can be generated to produce a vector using the seq function:

> seq(10)		# [1]  1  2  3  4  5  6  7  8  9 10
> seq(1, 10)		# [1]  1  2  3  4  5  6  7  8  9 10
> seq(length=10)	# [1]  1  2  3  4  5  6  7  8  9 10
> seq(2, 10, 2)	        # [1]  2  4  6  8 10
> seq(10, 2, -2)	# [1] 10  8  6  4  2
> seq(length = 0)	# numeric(0)
> seq(0)		# [1] 1 0
> seq(0, 1, by=.1)
> seq(0, 1, length=11)
> 1:10			# [1]  1  2  3  4  5  6  7  8  9 10

R will operate on vectors whenever they are given as arguments.

> c(2, 4, 6, 8, 10)/2			# [1] 1 2 3 4 5
> c(2, 4, 6, 8, 10)/c(1, 2, 3, 4, 5)	# [1] 2 2 2 2 2
> log(c(0.1, 1, 10, 100), 10)		# [1] -1  0  1  2

In vector operations, short vectors are recycled when additional values are required, but the longer vector's length must be a multiple of the shorter vector's length.

> c(1, 2, 3, 4) + c(1, 2)		# [1] 2 4 4 6
> c(1, 2, 3, 4, 5) + c(1, 2)
[1] 2 4 4 6 6
Warning message:
longer object length
    is not a multiple of shorter object length in: 
    c(1, 2, 3, 4, 5) + c(1, 2)



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