Preserve element names in multi-dimensional subsetting

[HenrikBengtsson]

Background

Vectors in can have dimensions and corresponding names, cf. dim() and dimnames(). They can concurrently have element names, cf. names(). For instance,

> x <- matrix(1:6, nrow=2)
> rownames(x) <- c("A", "B")
> colnames(x) <- c("X", "Y", "Z")
> names(x) <- letters[1:6]
> x
  X Y Z
A 1 3 5
B 2 4 6
attr(,"names")
[1] "a" "b" "c" "d" "e" "f"

This allows us to access elements both by dimensional names as by element names, e.g.

> x[3]
c
3
> x["c"]
c
3
> x[1,2]
[1] 3
> x["A","Y"]
[1] 3

Problem

When subsetting by dimensions, we loose the element names, e.g.

> y <- x[,2:3]
> y
  Y Z
A 3 5
B 4 6
> names(y)
NULL

Wish

Preserve element names also when subsetting by dimensions, e.g.

> y
  Y Z
A 3 5
B 4 6
attr(,"names")
[1] "c" "d" "e" "f"
> y[1]
c
3
> y["c"]
c
3