rep
Replicate Elements of Vectors and Lists
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. They are not generic.
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
reponly) aPOSIXctorPOSIXltorDateobject; 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- A integer 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 orNAvalues are an error. length.out- non-negative integer. The desired length of the
output vector. Other inputs will be coerced to an integer
vector and the first element taken. Ignored if
NAor invalid. each- non-negative integer. Each element of
xis repeatedeachtimes. Other inputs will be coerced to an integer vector and the first element taken. Treated as1ifNAor invalid.
- times
- see
.... - length.out
- non-negative integer: the desired length of the output vector.
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. R 2.x.y accepted pairlists and some other objects (although the results were rarely what their users intended).
References
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
See Also
Examples
library(base)
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)