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# Vector recycling
x <- 1:6
y <- c(10, 100)            # length 2 recycled to match length 6
x + y                      # 11 102 13 104 15 106

# Recycling with a scalar (length 1 recycles perfectly)
x * 2                      # 2 4 6 8 10 12
x - mean(x)                # centre the vector

# Warning when lengths are not multiples
# c(1,2,3,4,5) + c(1,2)   # warns: longer not multiple of shorter

# Lists: heterogeneous containers
person <- list(
    name   = "Diana",
    age    = 28,
    scores = c(90, 85, 92),
    active = TRUE
)

person[["name"]]    # "Diana"    — double bracket returns the element
person$age          # 28         — dollar-sign shorthand
person["scores"]    # a list containing the scores vector (single bracket)
person[["scores"]]  # the numeric vector itself

# Modifying list elements
person$city <- "Paris"
person[["age"]] <- 29

# Nested lists
nested <- list(a = list(b = list(c = 42)))
nested$a$b$c        # 42

# Factors
status <- factor(c("low", "med", "high", "med", "low"))
levels(status)      # "high" "low" "med"  (alphabetical by default)
nlevels(status)     # 3
table(status)       # frequency count

# Ordered factor
size <- ordered(c("S", "M", "L", "XL", "M"),
                levels = c("S", "M", "L", "XL"))
size[1] < size[3]   # TRUE  (S < L)