R Nuts and Bolts
Entering Input
x <- 1 #The <- symbol is the assignment operator.
Evaluation
When a complete expression is entered at the prompt, it is evaluated and the result of the evaluated
expression is returned.
R Objects
R has five basic or “atomic” classes of objects:
- character
- numeric (real numbers)
- integer
- complex
- logical (True/False)
vector:
A vector can only contain objects of the same class.
Numbers
Numbers in R a generally treated as numeric objects (i.e. double precision real numbers).
If you explicitly want an integer, you need to specify the L suffix.
Inf represents infinity;can be used in ordinary calculations
NaN an undefined value (“not a number”); e.g. 0 / 0
Attributes
- names, dimnames
- dimensions (e.g. matrices, arrays)
- class (e.g. integer, numeric)
- length
- other user-defined attributes/metadata
Creating Vectors
c() function
vector() function
x <- vector("numeric", length = 10)
Mixing Objects
implicit coercion
y <- c(1.7, "a") ## character
y <- c(TRUE, 2) ## numeric
y <- c("a", TRUE) ## character
Explicit Coercion
as.* functions
as.numeric(x)
as.logical(x)
as.character(x)
Matrices
m <- matrix(nrow = 2, ncol = 3)
m <- matrix(1:6, nrow = 2, ncol = 3)
Matrices are constructed column-wise, so entries can be thought of starting in the “upper left” corner and running down the columns.
m <- 1:10
dim(m) <- c(2, 5)
cbind()
rbind()
Lists
Lists are a special type of vector that can contain elements of different classes.
x <- list(1, "a", TRUE, 1 + 4i)
x <- vector("list", length = 5) # create an empty list of a prespecified length
Factors
x <- factor(c("yes", "yes", "no", "yes", "no"))
x <- factor(c("yes", "yes", "no", "yes", "no"), levels = c("yes", "no"))
Missing Values
Missing values are denoted by NA or NaN for q undefined mathematical operations.
- is.na() is used to test objects if they are NA
- is.nan() is used to test for NaN
- NA values have a class also, so there are integer NA, character NA, etc.
- A NaN value is also NA but the converse is not true
Data Frames
x <- data.frame(foo = 1:4, bar = c(T, T, F, F))
Names
vector list names()
| Object | Set column names | Set row names |
|---|---|---|
| data frame | names | row.names() |
| matrix | colnames() | rownames() |
