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rsubsetr-bigmemory

Proper way to subset big.matrix

I would like to know if there is a 'proper' way to subset big.matrix objects in R. It is simple to subset a matrix but the class always reverts to 'matrix'. This isn't a problem when working with small datasets like this but with massive datasets but with extremely large datasets the subset could still benefit from the 'big.matrix' class.

require(bigmemory)
data(iris)
# I realize the warning about factors but not important for this example
big <- as.big.matrix(iris)

class(big)
[1] "big.matrix"
attr(,"package")
[1] "bigmemory"

class(big[,c("Sepal.Length", "Sepal.Width")])
[1] "matrix"

class(big[,1:2])
[1] "matrix"
Solution

  • I have since learned that the 'proper' way to subset a big.matrix is to use sub.big.matrix although this is only for contiguous columns and/or rows. Non-contiguous subsetting is not currently implemented.

    sm <- sub.big.matrix(big, firstCol=1, lastCol=2)