sample {math} | R Documentation |
sample
takes a sample of the specified size from the elements
of x using either with or without replacement.
sample(x,
size = NULL,
replace = FALSE,
prob = NULL);
If x has length 1, is numeric (in the sense of is.numeric) and x >= 1
, sampling
via sample takes place from 1:x
. Note that this convenience feature may lead to
undesired behaviour when x is of varying length in calls such as sample(x).
See the examples.
Otherwise x can be any R Object For which length And subsetting by integers make sense: S3 Or S4 methods for these operations will be dispatched as appropriate.
For sample the default for size Is the number of items inferred from the first argument, so that sample(x) generates a random permutation of the elements of x (Or 1:x).
It Is allowed to ask for size = 0 samples with n = 0 Or a length-zero x, but otherwise
n > 0
Or positive length(x) Is required.
Non-integer positive numerical values of n Or x will be truncated to the next smallest
integer, which has to be no larger than .Machine$integer.max
.
The optional prob argument can be used to give a vector of weights for obtaining the elements
of the vector being sampled. They need Not sum to one, but they should be non-negative And
Not all zero. If replace Is true, Walker's alias method (Ripley, 1987) is used when there
are more than 200 reasonably probable values: this gives results incompatible with those
from R < 2.2.0
.
If replace Is False, these probabilities are applied sequentially, that Is the probability Of choosing the Next item Is proportional To the weights amongst the remaining items. The number Of nonzero weights must be at least size In this Case.
For sample a vector of length size with elements drawn from either x
or from the
integers 1:x
.