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R: Converting simple_triplet_matrix to other sparse matrix formats.

When working with the tm package in R, it produces a DocumentTermMatrix or TermDocumentMatrix as an S3 object of class simple_triplet_matrix from the package slam. Now R has various different packages for creating sparse matrices, each of which have packages depending upon themselves. Long back when working with text data I had created two functions to convert a simple_triplet_matrix to a matrix of class sparseMatrix (package: Matrix) and that to a matrix of class matrix.csr (package: SparseM). The conversions are simple enough once you have read through the documentation of the three packages but hopefully this will save someone some time.

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asSparseMatrix = function (simpleTripletMatrix) {
  retVal = sparseMatrix(i=simpleTripletMatrix[["i"]],
                        j=simpleTripletMatrix[["j"]],
                        x=simpleTripletMatrix[["v"]],
                        dims=c(simpleTripletMatrix[["nrow"]],
                               simpleTripletMatrix[["ncol"]]))
  if (!is.null(simpleTripletMatrix[["dimnames"]]))
    dimnames(retVal) = simpleTripletMatrix[["dimnames"]]
  return(retVal)
}

asMatrixCSR = function (sparseMatrix) {
  warning("Will lose dimnames!")
  as.matrix.csr(new("matrix.csc",
                    ra=sparseMatrix@x,
                    ja=sparseMatrix@i + 1L,
                    ia=sparseMatrix@p + 1L,
                    dimension=sparseMatrix@Dim))
}