R: Return first or last element of an object

first {gdata} | R Documentation

## Return first or last element of an object

### 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 greg@warnes.net

### 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

[Package gdata version 2.18.0 Index]