Factors: Representing categorical data

TODO

link to recode for changing factor levels and for transforming continuous variables into factors

wants <- c("DescTools")
has   <- wants %in% rownames(installed.packages())
if(any(!has)) install.packages(wants[!has])

sex     <- c("m", "f", "f", "m", "m", "m", "f", "f")
(sexFac <- factor(sex))

[1] m f f m m m f f
Levels: f m

factor(c(1, 1, 3, 3, 4, 4), levels=1:5)

[1] 1 1 3 3 4 4
Levels: 1 2 3 4 5

(sexNum <- rbinom(10, size=1, prob=0.5))

 [1] 0 0 0 0 0 1 1 0 1 0

factor(sexNum, labels=c("man", "woman"))

 [1] man   man   man   man   man   woman woman man   woman man  
Levels: man woman

levels(sexFac) <- c("female", "male")
sexFac

[1] male   female female male   male   male   female female
Levels: female male

(fac1 <- factor(rep(c("A", "B"), c(5, 5))))

 [1] A A A A A B B B B B
Levels: A B

(fac2 <- gl(2, 5, labels=c("less", "more"), ordered=TRUE))

 [1] less less less less less more more more more more
Levels: less < more

sample(fac2, length(fac2), replace=FALSE)

 [1] less more more less more less less less more more
Levels: less < more

expand.grid(IV1=gl(2, 2, labels=c("a", "b")), IV2=gl(3, 1))

nlevels(sexFac)

[1] 2

summary(sexFac)

female   male 
     4      4

levels(sexFac)

[1] "female" "male"

str(sexFac)

 Factor w/ 2 levels "female","male": 2 1 1 2 2 2 1 1

unclass(sexFac)

[1] 2 1 1 2 2 2 1 1
attr(,"levels")
[1] "female" "male"

unclass(factor(10:15))

[1] 1 2 3 4 5 6
attr(,"levels")
[1] "10" "11" "12" "13" "14" "15"

as.character(sexFac)

[1] "male"   "female" "female" "male"   "male"   "male"   "female" "female"

(fac1 <- factor(sample(LETTERS, 5)))

[1] B V A F O
Levels: A B F O V

(fac2 <- factor(sample(letters, 3)))

[1] w h q
Levels: h q w

(charVec1 <- levels(fac1)[fac1])

[1] "B" "V" "A" "F" "O"

(charVec2 <- levels(fac2)[fac2])

[1] "w" "h" "q"

factor(c(charVec1, charVec2))

[1] B V A F O w h q
Levels: A B F h O q V w

rep(fac1, times=2)

 [1] B V A F O B V A F O
Levels: A B F O V

Njk  <- 2
P    <- 2
Q    <- 3
(IV1 <- factor(rep(c("lo", "hi"), each=Njk*Q)))

 [1] lo lo lo lo lo lo hi hi hi hi hi hi
Levels: hi lo

(IV2 <- factor(rep(1:Q, times=Njk*P)))

 [1] 1 2 3 1 2 3 1 2 3 1 2 3
Levels: 1 2 3

interaction(IV1, IV2)

 [1] lo.1 lo.2 lo.3 lo.1 lo.2 lo.3 hi.1 hi.2 hi.3 hi.1 hi.2 hi.3
Levels: hi.1 lo.1 hi.2 lo.2 hi.3 lo.3

(status <- factor(c("hi", "lo", "hi", "mid")))

[1] hi  lo  hi  mid
Levels: hi lo mid

(ordStat <- ordered(status, levels=c("lo", "mid", "hi")))

[1] hi  lo  hi  mid
Levels: lo < mid < hi

ordStat[1] > ordStat[2]

[1] TRUE

(chars <- rep(LETTERS[1:3], each=5))

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

(fac1  <- factor(chars))

 [1] A A A A A B B B B B C C C C C
Levels: A B C

factor(chars, levels=c("C", "A", "B"))

 [1] A A A A A B B B B B C C C C C
Levels: C A B

library(DescTools)
(facRe <- reorder.factor(fac1, new.order=c("C", "B", "A")))

 [1] A A A A A B B B B B C C C C C
Levels: C B A

vec <- rnorm(15, rep(c(10, 5, 15), each=5), 3)
tapply(vec, fac1, FUN=mean)

        A         B         C 
11.236854  6.384761 13.134951

reorder(fac1, vec, FUN=mean)

 [1] A A A A A B B B B B C C C C C
Levels: B A C

(fac2 <- factor(sample(1:2, 10, replace=TRUE), labels=c("B", "A")))

 [1] B B A A A B B B B A
Levels: B A

sort(fac2)

 [1] B B B B B B A A A A
Levels: B A

sort(as.character(fac2))

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

try(detach(package:DescTools))