R14. New objects in R

mtcars is a built-in dataset in R. Only first 3 rows and first column are returned, in cars. The drop argument is given as FALSE, so a vector is not returned.

If you extract a column, etc, you are always creating new objects in R. Any changes on the new object do not affect the original object. While this might seem to lead to easier programming, it also makes R more memory intensive.

# ex14.R
# get only 3 row and 2 columns
cars <- mtcars[1:3,1,drop = FALSE]
cat("Original cars =\n")
print(cars)
mpg <- cars["mpg"]
cat("\nOriginal mpg =\n")
print(mpg)
mpg[1] <- 42
cat("\nModified mpg =\n")
print(mpg)
cat("\nMazda RX4 mpg is not modified\n")
cat("as mpg is a copy\n")
print(cars)
# Original cars =
#   mpg
# Mazda RX4     21.0
# Mazda RX4 Wag 21.0
# Datsun 710    22.8
# 
# Original mpg =
#   mpg
# Mazda RX4     21.0
# Mazda RX4 Wag 21.0
# Datsun 710    22.8
# 
# Modified mpg =
#   mpg
# Mazda RX4      42
# Mazda RX4 Wag  42
# Datsun 710     42
# 
# Mazda RX4 mpg is not modified
# as mpg is a copy
# mpg
# Mazda RX4     21.0
# Mazda RX4 Wag 21.0
# Datsun 710    22.8