Vectors

TODO

• link to generateData, transformData

Create vectors

Empty vectors

numeric(4)

[1] 0 0 0 0

character(3)

[1] "" "" ""

logical(5)

[1] FALSE FALSE FALSE FALSE FALSE

Create and combine vectors

Numeric vectors

(age <- c(18, 20, 30, 24, 23, 21))

[1] 18 20 30 24 23 21

addAge  <- c(27, 21, 19)
(ageNew <- c(age, addAge))

[1] 18 20 30 24 23 21 27 21 19

append(age, c(17, 31))

[1] 18 20 30 24 23 21 17 31

Character vectors

charVec1 <- c("Z", "Y", "X")
(charVec2 <- c(charVec1, "T", "S", "R"))

[1] "Z" "Y" "X" "T" "S" "R"

LETTERS[c(1, 2, 3)]

[1] "A" "B" "C"

letters[c(5, 9, 13)]

[1] "e" "i" "m"

(chars <- c("ipsum", "dolor", "sit"))

[1] "ipsum" "dolor" "sit"  

Information about vectors

length(age)

[1] 6

length(chars)

[1] 3

nchar(chars)

[1] 5 5 3

Extract and change vector elements

Extract elements with a numeric index

age[4]

[1] 24

age[4] <- 22
age

[1] 18 20 30 22 23 21

Get and change the last element

(ageLast <- age[length(age)])

[1] 21

age[length(age) + 1]

[1] NA

A vector does not need a name for getting one of its values

c(11, 12, 13, 14)[2]

[1] 12

Extract elements with index vectors

Get elements

idx <- c(1, 2, 4)
age[idx]

[1] 18 20 22

age[c(3, 5, 6)]

[1] 30 23 21

age[c(1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6)]

 [1] 18 18 20 20 30 30 22 22 23 23 21 21

age[c(4, NA, 1)]

[1] 22 NA 18

Change elements

age[idx] <- c(17, 30, 25)
age

[1] 17 30 30 25 23 21

Exclude elements

age[-3]

[1] 17 30 25 23 21

age[c(-1, -2, -4)]

[1] 30 23 21

age[-c(1, 2, 4)]

[1] 30 23 21

age[-idx]

[1] 30 23 21

Also see help(Extract)

Types of values in vectors

charVec4 <- "word"
numVec   <- c(10, 20, 30)
(combVec <- c(charVec4, numVec))

[1] "word" "10"   "20"   "30"  

mode(combVec)

[1] "character"

Named elements

(namedVec1 <- c(elem1="first", elem2="second"))

   elem1    elem2 
 "first" "second" 

namedVec1["elem1"]

  elem1 
"first" 

(namedVec2 <- c(val1=10, val2=-12, val3=33))

val1 val2 val3 
  10  -12   33 

names(namedVec2)

[1] "val1" "val2" "val3"

names(namedVec2) <- c("A", "B", "C")
namedVec2

  A   B   C 
 10 -12  33 

Delete elements

vec <- c(10, 20, 30, 40, 50)
vec <- vec[c(-4, -5)]
vec

[1] 10 20 30

vec <- c(1, 2, 3, 4, 5)
length(vec) <- 3
vec

[1] 1 2 3

Vector valued comparisons

Simple comparisons

age <- c(17, 30, 30, 24, 23, 21)
age < 24

[1]  TRUE FALSE FALSE FALSE  TRUE  TRUE

x <- c(2, 4, 8)
y <- c(3, 4, 5)
x == y

[1] FALSE  TRUE FALSE

x < y

[1]  TRUE FALSE FALSE

Information about elements satisfying some condition

res <- age > 30
any(res)

[1] FALSE

any(age < 18)

[1] TRUE

all(x == y)

[1] FALSE

res <- age < 24
sum(res)

[1] 3

which(age < 24)

[1] 1 5 6

length(which(age < 24))

[1] 3

Checking for equality of vectors

x <- c(4, 5, 6)
y <- c(4, 5, 6)
z <- c(1, 2, 3)
all.equal(x, y)

[1] TRUE

all.equal(y, z)

[1] "Mean relative difference: 0.6"

isTRUE(all.equal(y, z))

[1] FALSE

Combine multiple logical comparisons

(age <= 20) | (age >= 30)

[1]  TRUE  TRUE  TRUE FALSE FALSE FALSE

(age > 20) & (age < 30)

[1] FALSE FALSE FALSE  TRUE  TRUE  TRUE

Logical index vectors

Simple and combined selection criteria

age[c(TRUE, FALSE, TRUE, TRUE, FALSE, TRUE)]

[1] 17 30 24 21

(idx <- (age <= 20) | (age >= 30))

[1]  TRUE  TRUE  TRUE FALSE FALSE FALSE

age[idx]

[1] 17 30 30

age[(age >= 30) | (age <= 20)]

[1] 17 30 30

The recycling rule

age[c(TRUE, FALSE)]

[1] 17 30 23

age[c(TRUE, FALSE, TRUE, FALSE, TRUE, FALSE)]

[1] 17 30 23

Convert logical index vectors to numerical ones

Problem:

vecNA   <- c(-3, 2, 0, NA, -7, 5)
(logIdx <- vecNA > 0)

[1] FALSE  TRUE FALSE    NA FALSE  TRUE

vecNA[logIdx]

[1]  2 NA  5

Solution:

(numIdx <- which(logIdx))

[1] 2 6

vecNA[numIdx]

[1] 2 5

seq(along=logIdx) %in% numIdx

[1] FALSE  TRUE FALSE FALSE FALSE  TRUE

Get the article source from GitHub

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