Factors and Missing Values

install.packages('tinytex')
tinytex::install_tinytex()  # install TinyTeX

1 R chunk

x <- c(1,2,0/0, -5/0, -6, NA)
x

[1]    1    2  NaN -Inf   -6   NA

is.na(x)

[1] FALSE FALSE  TRUE FALSE FALSE  TRUE

is.nan(x)

[1] FALSE FALSE  TRUE FALSE FALSE FALSE

y <- c("Freshman", "Sophomore", "Junior", "Senior", "Freshman", "Junior", "Junior")
y

[1] "Freshman"  "Sophomore" "Junior"    "Senior"    "Freshman" 
[6] "Junior"    "Junior"   

typeof(y)

[1] "character"

z <- factor(y)
z

[1] Freshman  Sophomore Junior    Senior    Freshman  Junior   
[7] Junior   
Levels: Freshman Junior Senior Sophomore

table(z)

z
 Freshman    Junior    Senior Sophomore 
        2         3         1         1