"x" means the letter x, x means the
object x. Similarly, 1 means the number one and "1" means
the symbol used for the number one.
A vector is a set of scalars arranged in a one dimensional array (or alternatively, scalars are vectors of length 1). Vectors can only contain one type of scalar: either numbers or characters but not both. If S-PLUS sees both in the same vector it will change the numeric arguments to characters (by enclosing them in quotes).
> blah <- c(1,2,3,"d") > blah [1] "1" "2" "3" "d"In the example above, S-PLUS converted the numbers 1,2 and 3 to their respective symbols so that all four elements in
blah
would be characters.
Use subscripts to see or change the value of a particular element or elements of a vector (this is covered in ``Introduction to S-PLUS'').
> blah[1] [1] "1" > blah[c(1,2,3)] [1] "1" "2" "3" > blah[4] [1] "d" > blah[4] <- "zip" > blah [1] "1" "2" "3" "zip"Vectors have a length attribute, which can be viewed or changed by using the function
length.
> length(blah) [1] 4 > length(blah) <- 5 > blah [1] "1" "2" "3" "zip" ""Note that when
blah was changed to length five, the blank character
("") was added to the end of the vector as the fifth element. Had
blah been a numeric vector, the new element would have been the blank
numeric element (``NA'', for Not Available).
Question: What happens when you reduce the length of a vector?