adiag {magic}

Binds arrays corner-to-corner

Description

Array generalization of blockdiag()

Usage

adiag(... , pad=as.integer(0), do.dimnames=TRUE)

Arguments

...

Arrays to be binded together

pad

Value to pad array with; note default keeps integer status of arrays

do.dimnames

Boolean, with default TRUE meaning to return dimnames if possible. Set to FALSE if performance is an issue

Details

Binds any number of arrays together, corner-to-corner. Because the function is associative provided pad is of length 1, this page discusses the two array case.

Suppose x <- adiag(a,b) and dim(a)=c(a_1,...,a_d), dim(b)=c(b_1,...,b_d). Then we have all(dim(x)==dim(a)+dim(b)); and x[1:a_1,...,1:a_d]==a and x[(a_1+1):(a_1+b_1),...,(a_d+1):(a_d+b_d)]==b.

Dimnames are preserved, if both arrays have non-null dimnames, and do.dimnames is TRUE.

Argument pad is usually a length-one vector, but any vector is acceptable; standard recycling is used. Be aware that the output array (of dimension dim(a)+dim(b)) is filled with (copies of) pad before a and b are copied. This can be confusing.

Value

Returns an array of dimensions dim(a)+dim(b) as described above.

Note

In adiag(a,b), if a is a length-one vector, it is coerced to an array of dimensions rep(1,length(dim(b))); likewise b. If both a and b are length-one vectors, return diag(c(a,b)).

If a and b are arrays, function adiag() requires length(dim(a))==length(dim(b)) (the function does not guess which dimensions have been dropped; see examples section). In particular, note that vectors are not coerced except if of length one.

adiag() is used when padding magic hypercubes in the context of evaluating subarray sums.

Author(s)

Peter Wolf with some additions by Robin Hankin

See Also

subsums, apad

Examples

 a <- array( 1,c(2,2))
 b <- array(-1,c(2,2))
 adiag(a,b)

 ## dropped dimensions can count:

 b2 <- b1 <- b
 dim(a) <- c(2,1,2)
 dim(b1) <- c(2,2,1)
 dim(b2) <- c(1,2,2)

 dim(adiag(a,b1))
 dim(adiag(a,b2))

## dimnames are preserved if not null:

a <- matrix(1,2,2,dimnames=list(col=c("red","blue"),size=c("big","small"))) 
b <- 8
dim(b) <- c(1,1)
dimnames(b) <- list(col=c("green"),size=c("tiny"))
adiag(a,b)   #dimnames preserved
adiag(a,8)   #dimnames lost because second argument has none.

## non scalar values for pad can be confusing:
q <- matrix(0,3,3)
adiag(q,q,pad=1:4)

## following example should make the pattern clear:
adiag(q,q,pad=1:36)


# Now, a use for arrays with dimensions of zero extent:
z <- array(dim=c(0,3))
colnames(z) <- c("foo","bar","baz")

adiag(a,z)        # Observe how this has
                  # added no (ie zero) rows to "a" but
                  # three extra columns filled with the pad value

adiag(a,t(z))
adiag(z,t(z))     # just the pad value