first: Return first or last element of an object

In gdata: Various R Programming Tools for Data Manipulation

Description

Return first or last element of an object. These functions are convenience wrappers for head(x, n=1, ...) and tail(x, n=1, ...).

Usage

first(x, n=1, ...)
last(x, n=1, ...)
first(x, n=1, ...) <- value
last(x, n=1, ...) <- value

Arguments

x	data object
n	a single integer. If positive, size for the resulting object: number of elements for a vector (including lists), rows for a matrix or data frame or lines for a function. If negative, all but the 'n' last/first number of elements of 'x'.
...	arguments to be passed to or from other methods.
value	a vector of values to be assigned (should be of length n)

Value

An object (usually) like 'x' but generally smaller.

Author(s)

Gregory R. Warnes [e-mail]

See Also

head, tail, left, right

Examples

## works for vectors..
v <- 1:10
first(v)
last(v)

first(v) <- 9
v

last(v) <- 20
v

## and for lists
l <- list(a=1, b=2, c=3)
first(l)
last(l)

first(l) <- "apple"
last(l)  <- "bannana"
l

## and data.frames
df <- data.frame(a=1:2, b=3:4, c=5:6)
first(df)
last(df)

first(df) <- factor(c("red","green"))
last(df) <- list(c(20,30)) # note the enclosing list!
df

## and matrixes
m <- as.matrix(df)
first(m)
last(m)

first(m) <- "z"
last(m)  <- "q"
m

gdata documentation built on May 2, 2019, 5:49 p.m.