Combine multi-dimensional arrays
Combine multi-dimensional arrays. This is a generalization of cbind and rbind. Takes a sequence of vectors, matrices, or arrays and produces a single array of the same or higher dimension.
abind(..., along=N, rev.along=NULL, new.names=NULL, force.array=TRUE, make.names=use.anon.names, use.anon.names=FALSE, use.first.dimnames=FALSE, hier.names=FALSE, use.dnns=FALSE)
- Any number of vectors, matrices, arrays, or data frames.
The dimensions of all the arrays must match, except on one dimension
along=). If these arguments are named, the name will be used for the name of the dimension along which the arrays are joined. Vectors are treated as having a dim attribute of length one.
Alternatively, there can be one (and only one) list argument supplied, whose components are the objects to be bound together. Names of the list components are treated in the same way as argument names.
- (optional) The dimension along which to bind the arrays.
The default is the last dimension, i.e., the maximum length of the dim
attribute of the supplied arrays.
along=can take any non-negative value up to the minimum length of the dim attribute of supplied arrays plus one. When
along=has a fractional value, a value less than 1, or a value greater than N (N is the maximum of the lengths of the dim attribute of the objects to be bound together), a new dimension is created in the result. In these cases, the dimensions of all arguments must be identical.
Alternate way to specify the dimension along which to bind the arrays:
along = N + 1 - rev.along. This is provided mainly to allow easy specification of
along = N + 1(by supplying
rev.along=0). If both
rev.alongare supplied, the supplied value of
If new.names is a list, it is the first choice for the
dimnames attribute of the result. It should have the same
structure as a dimnames attribute. If the names for a
particular dimension are
NULL, names for this dimension are constructed in other ways.
new.namesis a character vector, it is used for dimension names in the same way as argument names are used. Zero length ("") names are ignored.
- (optional) If
FALSE, rbind or cbind are called when possible, i.e., when the arguments are all vectors, and along is not 1, or when the arguments are vectors or matrices or data frames and along is 1 or 2. If rbind or cbind are used, they will preserve the data.frame classes (or any other class that r/cbind preserve). Otherwise, abind will convert objects to class array. Thus, to guarantee that an array object is returned, supply the argument
force.array=TRUE. Note that the use of rbind or cbind introduces some subtle changes in the way default dimension names are constructed: see the examples below.
TRUE, the last resort for dimnames for the along dimension will be the deparsed versions of anonymous arguments. This can result in cumbersome names when arguments are expressions.
The default is
use.anon.namesis a deprecated synonym for
When dimension names are present on more than one
argument, should dimension names for the result be take from
the first available (the default is to take them from the
last available, which is the same behavior as
TRUE, dimension names on the concatenated dimension will be composed of the argument name and the dimension names of the objects being bound. If a single list argument is supplied, then the names of the components serve as the argument names.
hier.namescan also have values
"after"; these determine the order in which the argument name and the dimension name are put together (
TRUEhas the same effect as
FALSE) Use names on dimensions, e.g., so that
names(dimnames(x))is non-empty. When there are multiple possible sources for names of dimnames, the value of
use.first.dimnamesdetermines the result.
The dimensions of the supplied vectors or arrays do not need
to be identical, e.g., arguments can be a mixture of vectors
abind coerces arguments by the addition
of one dimension in order to make them consistent with other
along=. The extra dimension is
added in the place specified by
The default action of abind is to concatenate on the last
dimension, rather than increase the number of dimensions.
For example, the result of calling abind with vectors is a
longer vector (see first example below). This differs from
the action of
rbind and cbind which is to return a matrix when
called with vectors. abind can be made to behave like cbind
on vectors by specifying
along=2, and like rbind by
The dimnames of the returned object are pieced together
from the dimnames of the arguments, and the names of the
arguments. Names for each dimension are searched for in the
following order: new.names, argument name, dimnames (or
names) attribute of last argument, dimnames (or names)
attribute of second last argument, etc. (Supplying the
use.first.dimnames=TRUE changes this to
abind to use dimnames or names from the
first argument first. The default behavior is the same as
cbind: use dimnames
from later arguments.) If some names are supplied for the
along dimension (either as argument names or dimnames in
arguments), names are constructed for anonymous arguments
- An array with a dim attribute calculated as follows.Let
rMin=min(sapply(list(...), function(x) length(dim(x))))and
rMax=max(sapply(list(...), function(x) length(dim(x))))(where the length of the dimensions of a vector are taken to be 1). Then
rMaxshould be equal to or one greater than
alongrefers to an existing dimension, then the length of the dim attribute of the result is
alongdoes not refer to an existing dimension, then
rMinand the length of the dim attribute of the result will be
cbindare called to compute the result if (a)
force.array=FALSE; and (b) the result will be a two-dimensional object.
It would be nice to make
abind() an S3 generic, but S3 generics
cannot dispatch off anonymous arguments.
The ability of
abind() to accept a single list argument removes
much of the need for constructs like
list.of.arrays). Instead, just do
direct construct is preferred because
do.call() construct can
sometimes consume more memory during evaluation.
# Five different ways of binding together two matrices x <- matrix(1:12,3,4) y <- x+100 dim(abind(x,y,along=0)) # binds on new dimension before first dim(abind(x,y,along=1)) # binds on first dimension dim(abind(x,y,along=1.5)) dim(abind(x,y,along=2)) dim(abind(x,y,along=3)) dim(abind(x,y,rev.along=1)) # binds on last dimension dim(abind(x,y,rev.along=0)) # binds on new dimension after last # Unlike cbind or rbind in that the default is to bind # along the last dimension of the inputs, which for vectors # means the result is a vector (because a vector is # treated as an array with length(dim(x))==1). abind(x=1:4,y=5:8) # Like cbind abind(x=1:4,y=5:8,along=2) abind(x=1:4,matrix(5:20,nrow=4),along=2) abind(1:4,matrix(5:20,nrow=4),along=2) # Like rbind abind(x=1:4,matrix(5:20,nrow=4),along=1) abind(1:4,matrix(5:20,nrow=4),along=1) # Create a 3-d array out of two matrices abind(x=matrix(1:16,nrow=4),y=matrix(17:32,nrow=4),along=3) # Use of hier.names abind(x=cbind(a=1:3,b=4:6), y=cbind(a=7:9,b=10:12), hier.names=TRUE) # Use a list argument abind(list(x=x, y=x), along=3) # Use lapply(..., get) to get the objects an <- c('x','y') names(an) <- an abind(lapply(an, get), along=3)