Return first or last element of an object
Return first or last element of an object. These functions are convenience
wrappers for head(x, n=1, ...) and tail(x, n=1, ...).
first(x, n=1, ...) last(x, n=1, ...) first(x, n=1, ...) <- value last(x, n=1, ...) <- value
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 |
An object (usually) like 'x' but generally smaller.
Gregory R. Warnes greg@warnes.net
## 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"
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