R: Replicate Elements of Vectors and Lists

rep {base} | R Documentation

## Replicate Elements of Vectors and Lists

### Description

`rep` replicates the values in `x`. It is a generic function, and the (internal) default method is described here.

`rep.int` and `rep_len` are faster simplified versions for two common cases. Internally, they are generic, so methods can be defined for them (see InternalMethods).

### Usage

    rep(x, ...)

    rep.int(x, times)

    rep_len(x, length.out)

### Arguments

`x` | a vector (of any mode including a `list`) or a factor or (for `rep` only) a `POSIXct` or `POSIXlt` or `Date` object; or an S4 object containing such an object.
`...` | further arguments to be passed to or from other methods. For the internal default method these can include: `times` an integer-valued vector giving the (non-negative) number of times to repeat each element if of length `length(x)`, or to repeat the whole vector if of length 1. Negative or `NA` values are an error. A `double` vector is accepted, other inputs being coerced to an integer or double vector. `length.out` non-negative integer. The desired length of the output vector. Other inputs will be coerced to a double vector and the first element taken. Ignored if `NA` or invalid. `each` non-negative integer. Each element of `x` is repeated `each` times. Other inputs will be coerced to an integer or double vector and the first element taken. Treated as `1` if `NA` or invalid.
`times, length.out` | see `...` above.

### Details

The default behaviour is as if the call was

      rep(x, times = 1, length.out = NA, each = 1)

. Normally just one of the additional arguments is specified, but if `each` is specified with either of the other two, its replication is performed first, and then that implied by `times` or `length.out`.

If `times` consists of a single integer, the result consists of the whole input repeated this many times. If `times` is a vector of the same length as `x` (after replication by `each`), the result consists of `x[1]` repeated `times[1]` times, `x[2]` repeated `times[2]` times and so on.

`length.out` may be given in place of `times`, in which case `x` is repeated as many times as is necessary to create a vector of this length. If both are given, `length.out` takes priority and `times` is ignored.

Non-integer values of `times` will be truncated towards zero. If `times` is a computed quantity it is prudent to add a small fuzz or use `round`. And analogously for `each`.

If `x` has length zero and `length.out` is supplied and is positive, the values are filled in using the extraction rules, that is by an `NA` of the appropriate class for an atomic vector (`0` for raw vectors) and `NULL` for a list.

### Value

An object of the same type as `x`.

`rep.int` and `rep_len` return no attributes (except the class if returning a factor).

The default method of `rep` gives the result names (which will almost always contain duplicates) if `x` had names, but retains no other attributes.

### Note

Function `rep.int` is a simple case which was provided as a separate function partly for S compatibility and partly for speed (especially when names can be dropped). The performance of `rep` has been improved since, but `rep.int` is still at least twice as fast when `x` has names.

The name `rep.int` long precedes making `rep` generic.

Function `rep` is a primitive, but (partial) matching of argument names is performed as for normal functions.

For historical reasons `rep` (only) works on `NULL`: the result is always `NULL` even when `length.out` is positive.

Although it has never been documented, these functions have always worked on expression vectors.

### References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.

### See Also

`seq`, `sequence`, `replicate`.

### Examples

    rep(1:4, 2)
    rep(1:4, each = 2)       # not the same.
    rep(1:4, c(2,2,2,2))     # same as second.
    rep(1:4, c(2,1,2,1))
    rep(1:4, each = 2, len = 4)    # first 4 only.
    rep(1:4, each = 2, len = 10)   # 8 integers plus two recycled 1's.
    rep(1:4, each = 2, times = 3)  # length 24, 3 complete replications

    rep(1, 40*(1-.8)) # length 7 on most platforms
    rep(1, 40*(1-.8)+1e-7) # better

    ## replicate a list
    fred <- list(happy = 1:10, name = "squash")
    rep(fred, 5)

    # date-time objects
    x <- .leap.seconds[1:3]
    rep(x, 2)
    rep(as.POSIXlt(x), rep(2, 3))

    ## named factor
    x <- factor(LETTERS[1:4]); names(x) <- letters[1:4]
    x
    rep(x, 2)
    rep(x, each = 2)
    rep.int(x, 2)  # no names
    rep_len(x, 10)

[Package base version 4.0.5 Index]