The Art of R Programming

$c

[1] "sailing"

[[3]]

[1] 28

[[4]]

[1] FALSE

[[5]]

[1] TRUE

[[6]]

[1] TRUE

Note that upon deletingz$b, the indices of the elements after it moved

up by 1. For instance, the formerz[[4]]becamez[[3]].

You can also concatenate lists.

> c(list("Joe", 55000, T),list(5))

[[1]]

[1] "Joe"

[[2]]

[1] 55000

[[3]]

[1] TRUE

[[4]]

[1] 5

4.2.3 Getting the Size of a List.........................................

Since a list is a vector, you can obtain the number of components in a list via

length().

> length(j)

[1] 3

4.2.4 Extended Example: Text Concordance............................

Web search and other types of textual data mining are of great interest

today. Let’s use this area for an example of R list code.

We’ll write a function calledfindwords()that will determine which words

are in a text file and compile a list of the locations of each word’s occur-

rences in the text. This would be useful for contextual analysis, for example.

90 Chapter 4