Generate a set of permutations from the specified design.
shuffleSet returns a set of nset permutations from the
specified design. The main purpose of the function is to circumvent
the overhead of repeatedly calling shuffle to generate a
set of permutations.
shuffleSet(n, nset, control = how(), check = TRUE, quietly = FALSE) ## S3 method for class 'permutationMatrix' as.matrix(x, ...)
n |
numeric; the number of observations in the sample set. May also be
any object that |
nset |
numeric; the number of permutations to generate for the set. Can be
missing, the default, in which case |
control |
an object of class |
check |
logical; should the design be checked for various problems via
function |
quietly |
logical; should messages by suppressed? |
x |
an object of class |
... |
arguments passed to other methods. For the |
shuffleSet is designed to generate a set of nset
permutation indices over which a function can iterate as part of a
permutation test. It is only slightly more efficient than calling
shuffle nset times, but it is far more practical
than the simpler function because a set of permutations can be worked
on by applying a function to the rows of the returned object. This
simplifies the function applied, and facilitates the use of parallel
processing functions, thus enabling a larger number of permutations to
be evaluated in reasonable time.
By default, shuffleSet will check the permutations design
following a few simple heuristics. See check for details
of these. Whether some of the heuristics are activiated or not can be
controlled via how, essentialy via its argument
minperm. In particular, if there are fewer than minperm
permutations, shuffleSet will generate and return all
possible permutations, which may differ from the number requested via
argument nset.
The check argument to shuffleSet controls whether
checking is performed in the permutation design. If you set
check = FALSE then exactly nset permutations will be
returned. However, do be aware that there is no guarantee that the set
of permutations returned will be unique, especially so for designs and
data sets where there are few possible permutations relative to the
number requested.
The as.matrix method sets the control and seed
attributes to NULL and removes the "permutationMatrix"
class, resulting in a standard matrix object.
Returns a matrix of permutations, where each row is a separate
permutation. As such, the returned matrix has nset rows and
n columns.
Gavin L. Simpson
shuffleSet() is modelled after the permutation schemes of Canoco
3.1 (ter Braak, 1990); see also Besag & Clifford (1989).
Besag, J. and Clifford, P. (1989) Generalized Monte Carlo significance tests. Biometrika 76; 633–642.
ter Braak, C. J. F. (1990). Update notes: CANOCO version 3.1. Wageningen: Agricultural Mathematics Group. (UR).
set.seed(1)
## simple random permutations, 5 permutations in set
shuffleSet(n = 10, nset = 5)
## series random permutations, 5 permutations in set
shuffleSet(10, 5, how(within = Within(type = "series")))
## series random permutations, 10 permutations in set,
## with possible mirroring
CTRL <- how(within = Within(type = "series", mirror = TRUE))
shuffleSet(10, 10, CTRL)
## Permuting strata
## 4 groups of 5 observations
CTRL <- how(within = Within(type = "none"),
plots = Plots(strata = gl(4,5), type = "free"))
shuffleSet(20, 10, control = CTRL)
## 10 random permutations in presence of Plot-level strata
plotStrata <- Plots(strata = gl(4,5))
CTRL <- how(plots = plotStrata,
within = Within(type = "free"))
numPerms(20, control = CTRL)
shuffleSet(20, 10, control = CTRL)
## as above but same random permutation within Plot-level strata
CTRL <- how(plots = plotStrata,
within = Within(type = "free", constant = TRUE))
numPerms(20, control = CTRL)
shuffleSet(20, 10, CTRL) ## check this.
## time series within each level of Plot strata
CTRL <- how(plots = plotStrata,
within = Within(type = "series"))
shuffleSet(20, 10, CTRL)
## as above, but with same permutation for each Plot-level stratum
CTRL <- how(plots = plotStrata,
within = Within(type = "series", constant = TRUE))
shuffleSet(20, 10, CTRL)Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.