The Art of R Programming

The Boolean valuesTRUEandFALSEcan be abbreviated asTandF

(both must be capitalized). These values change to 1 and 0 in arithmetic

expressions:

>1<2

[1] TRUE

>(1<2)*(3<4)

[1] 1

>(1<2)*(3<4)*(5<1)

[1] 0

> (1 < 2) == TRUE

[1] TRUE

>(1<2)==1

[1] TRUE

In the second computation, for instance, the comparison1<2returns

TRUE, and3<4yieldsTRUEas well. Both values are treated as 1 values, so the

product is 1.

On the surface, R functions look similar to those of C, Java, and so on.

However, they have much more of a functional programming flavor, which

has direct implications for the R programmer.

7.3 Default Values for Arguments................................................

In Section 5.1.2, we read in a data set from a file namedexams:

> testscores <- read.table("exams",header=TRUE)

The argumentheader=TRUEtells R that we have a header line, so R should

not count that first line in the file as data.

This is an example of the use ofnamed arguments. Here are the first few

lines of the function:

> read.table

function (file, header = FALSE, sep = "", quote = "\"'", dec = ".",

row.names, col.names, as.is = !stringsAsFactors, na.strings = "NA",

colClasses = NA, nrows = -1, skip = 0, check.names = TRUE,

fill = !blank.lines.skip, strip.white = FALSE, blank.lines.skip = TRUE,

comment.char = "#", allowEscapes = FALSE, flush = FALSE,

stringsAsFactors = default.stringsAsFactors(), encoding = "unknown")

{

if (is.character(file)) {

file <- file(file, "r")

on.exit(close(file))

...

...

146 Chapter 7