ภาพรวมระบบชนิดข้อมูลของ R

# Check class and type of various objects
cat('class(42L)    :', class(42L), '
')
cat('typeof(42L)   :', typeof(42L), '
')
cat('class(3.14)   :', class(3.14), '
')
cat('typeof(3.14)  :', typeof(3.14), '
')
cat('class(TRUE)   :', class(TRUE), '
')
cat('class("hello"):', class('hello'), '
')

m <- matrix(1:4, nrow = 2)
cat('class(matrix)  :', class(m), '
')   # matrix array
cat('typeof(matrix) :', typeof(m), '
')  # integer

f <- factor(c('a', 'b', 'a'))
cat('class(factor)  :', class(f), '
')   # factor
cat('typeof(factor) :', typeof(f), '
')  # integer (stored as int!)

cat('class(list)    :', class(list()), '
')  # list
cat('typeof(list)   :', typeof(list()), '
') # list

cat('is.numeric(3.14):', is.numeric(3.14), '
')    # TRUE (double)
cat('is.numeric(3L):  ', is.numeric(3L), '
')      # TRUE (integer)
cat('is.numeric(TRUE):', is.numeric(TRUE), '
')    # FALSE
cat('is.numeric("3"): ', is.numeric('3'), '
')     # FALSE
cat('is.numeric(NA):  ', is.numeric(NA), '
')      # FALSE (NA is logical)

x_int <- 5L
x_dbl <- 5.0

cat('--- x_int = 5L ---
')
cat('is.integer:', is.integer(x_int), '
')  # TRUE
cat('is.double: ', is.double(x_int), '
')   # FALSE
cat('is.numeric:', is.numeric(x_int), '
')  # TRUE

cat('--- x_dbl = 5.0 ---
')
cat('is.integer:', is.integer(x_dbl), '
')  # FALSE
cat('is.double: ', is.double(x_dbl), '
')   # TRUE
cat('is.numeric:', is.numeric(x_dbl), '
')  # TRUE

greetings <- c('hello', 'world', 'R')
numbers <- c(1, 2, 3)
numeric_string <- '42'

cat('is.character(greetings):      ', is.character(greetings), '
')
cat('is.character(numbers):        ', is.character(numbers), '
')
cat('is.character(numeric_string): ', is.character(numeric_string), '
')
cat('is.character(NA_character_):  ', is.character(NA_character_), '
')

flags <- c(TRUE, FALSE, TRUE, NA)
cat('is.logical(flags): ', is.logical(flags), '
')   # TRUE
cat('is.logical(NA):    ', is.logical(NA), '
')      # TRUE (default NA is logical)
cat('is.logical(1):     ', is.logical(1), '
')       # FALSE
cat('is.logical("TRUE"):', is.logical('TRUE'), '
')  # FALSE
cat('typeof(NA):        ', typeof(NA), '
')          # logical

# Type hierarchy in action
cat('c(TRUE, 1L) type:     ', typeof(c(TRUE, 1L)), '
')   # integer
cat('c(1L, 1.5) type:      ', typeof(c(1L, 1.5)), '
')   # double
cat('c(1.5, 1+0i) type:    ', typeof(c(1.5, 1+0i)), '
') # complex
cat('c(1+0i, "a") type:   ', typeof(c(1+0i, 'a')), '
')  # character
cat('c(TRUE, "x") type:    ', typeof(c(TRUE, 'x')), '
') # character

describe_type <- function(x, label) {
  cat(label, ': class =', class(x), ', typeof =', typeof(x),
      ', length =', length(x), '
')
}

describe_type(42L,         'integer literal')
describe_type(3.14,        'double literal')
describe_type(TRUE,        'logical')
describe_type('hello',     'character')
describe_type(c(1,2,3),    'numeric vector')
describe_type(list(1,'a'), 'list')

x_int <- 5L
x_dbl <- 5.0

cat('mode(5L):         ', mode(x_int), '
')          # numeric
cat('mode(5.0):        ', mode(x_dbl), '
')          # numeric
cat('storage.mode(5L): ', storage.mode(x_int), '
')  # integer
cat('storage.mode(5.0):', storage.mode(x_dbl), '
')  # double
# mode() lumps int+dbl; storage.mode() / typeof() distinguish them

df <- data.frame(
  id      = 1:3,
  name    = c('Alice', 'Bob', 'Carol'),
  score   = c(88.5, 79.0, 92.3),
  passed  = c(TRUE, TRUE, TRUE)
)
cat('Column types:
')
print(sapply(df, class))
cat('Column typeof:
')
print(sapply(df, typeof))

x <- 42L
cat('class(42L):       ', class(x), '
')
cat('typeof(42L):      ', typeof(x), '
')
cat('is.numeric(42L):  ', is.numeric(x), '
')
cat('is.integer(42L):  ', is.integer(x), '
')
cat('is.double(42L):   ', is.double(x), '
')
cat('is.character(42L):', is.character(x), '
')

# Type audit function
audit_types <- function(x, name = 'x') {
  cat(name, ': class=', class(x), ', typeof=', typeof(x),
      ', is.numeric=', is.numeric(x), '
')
}
audit_types(1L,      'integer')
audit_types(1.0,     'double')
audit_types(TRUE,    'logical')
audit_types('hello', 'character')
audit_types(1+2i,    'complex')