first: Return first or last element of an object

Description Usage Arguments Value Author(s) See Also Examples

View source: R/first.R

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

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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 greg@warnes.net

See Also

head, tail, left, right

Examples

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## 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 June 6, 2017, 5:04 p.m.