Data Analysis with R, Second Edition - Second Edition

Subsetting

It is very common to want to extract one or more elements from a vector. For this, we use a technique called indexing or subsetting. After the vector, we put an integer in square brackets ([]) called the subscript operator. This instructs R to return the element at that index. The indices (plural for index, in case you were wondering!) for vectors in R start at 1 and stop at the length of the vector:

  > our.vect[1]                  # to get the first value 
  [1] 8 
  > # the function length() returns the length of a vector 
  > length(our.vect) 
  [1] 7 
  > our.vect[length(our.vect)]   # get the last element of a vector 
  [1] 9 

Note that in the preceding code, we used a function in the subscript operator. In cases like these, R evaluates the expression in the ...