On Dec 4, 2009, at 3:52 PM, Austin Huang wrote:
One problem I've been having is the special case in which only one
row/column remains and the variable gets converted into a vector when
entries are removed by logical masking. This is a problem because
subsequent
code may rely on matrix operations (apply, colsums, dim, etc) For
example:
a <- matrix(c(1, 2, 3, 4), nrow = 2)
a
[,1] [,2]
[1,] 1 3
[2,] 2 4
rmask <- c(TRUE, FALSE)
b <- a[rmask, ]
colSums(b)
> b <- a[rmask, , drop=FALSE]
> colSums(b)
[1] 1 3
Error in colSums(b) : 'x' must be an array of at least two dimensions
To ensure the code works regardless of how the matrix gets modified,
I need
to explicitly recast results to a matrix, for example:
b <- matrix(a[rmask, ], ncol = 2)
This can get messy, requiring extra work to maintain column/row
names or
additional commands to determine the correct dimensions of the
matrix (for
example, if I'm masking both rows and columns simultaneously). Is
there a
more elegant way to deal with this in R?
--
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
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