Consistently subset matrix to a vector and avoid colnames?

Question

I would like to know if there is R syntax to extract a column from a matrix and always have no name attribute on the returned vector (I wish to rely on this behaviour).

My problem is the following inconsistency:

• when a matrix has more than one row and I do myMatrix[, 1] I will get the first column of myMatrix with no name attribute. This is what I want.
• when a matrix has exactly one row and I do myMatrix[, 1], I will get the first column of myMatrix but it has the first colname as its name.

I would like to be able to do myMatrix[, 1] and consistently get something with no name.

An example to demonstrate this:

# make a matrix with more than one row,
x <- matrix(1:2, nrow=2)
colnames(x) <- 'foo'
#      foo
# [1,]   1
# [2,]   2

# extract first column. Note no 'foo' name is attached.
x[, 1]
# [1] 1 2

# now suppose x has just one row (and is a matrix)
x <- x[1, , drop=F]
# extract first column
x[, 1]
# foo    # <-- we keep the name!!
#   1

Now, the documentation for [ (?'[') mentions this behaviour, so it's not a bug or anything (although, why?! why this inconsistency?!):

A vector obtained by matrix indexing will be unnamed unless ‘x’ is one-dimensional when the row names (if any) will be indexed to provide names for the result.

My question is, is there a way to do x[, 1] such that the result is always unnamed, where x is a matrix?

Is my only hope unname(x[, 1]) or is there something analogous to ['s drop argument? Or is there an option I can set to say "always unname"? Some trick I can use (somehow override ['s behaviour when the extracted result is a vector?)

Answer 1

Update on why the code below works (as far as I can tell)

Subsetting with [ is handled using functions contained in the R source file subset.c in ~/src/main. When using matrix indexing to subset a matrix, the function VectorSubset is called. When there is more than one index used (i.e., one each for rows and columns as in x[,1]), then MatrixSubset is called.

The function VectorSubset only assigns names to 1-dimensional arrays being subsetted. Since a matrix is a 2-D array, no names are assigned to the result when using matrix indexing. The function MatrixSubset, however, does attempt to pass on dimnames under certain circumstances.

---

Therefore, the matrix indexing you refer to in the quote from the help page seems to be the key:

x <- matrix(1)
colnames(x) <- "foo"
x[, 1]  ## 'Normal' indexing
# foo 
#   1 
x[matrix(c(1, 1), ncol = 2)]  ## Matrix indexing
# [1] 1

And with a wider 1-row matrix:

xx <- matrix(1:10, nrow = 1)
colnames(xx) <- sprintf('foo%i', seq_len(ncol(xx)))
xx[, 6]  ## 'Normal' indexing
# foo6 
#    6 
xx[matrix(c(1, 6), ncol = 2)]  ## Matrix indexing
# [1] 6

With a matrix with both dimensions > 1:

yy <- matrix(1:10, nrow = 2, dimnames = list(NULL,
  sprintf('foo%i', 1:5)))

yy[cbind(seq_len(nrow(yy)), 3)]  ## Matrix indexing
# [1] 5 6