Matrix (version 1.5-3)

sparse.model.matrix: Construct Sparse Design / Model Matrices


Construct a sparse model or “design” matrix, from a formula and data frame (sparse.model.matrix) or a single factor (fac2sparse).

The fac2[Ss]parse() functions are utilities, also used internally in the principal user level function sparse.model.matrix().


sparse.model.matrix(object, data = environment(object),
		    contrasts.arg = NULL, xlev = NULL, transpose = FALSE,
		    drop.unused.levels = FALSE, row.names = TRUE,
		    sep = "", verbose = FALSE, ...)

fac2sparse(from, to = c("d", "l", "n"), drop.unused.levels = TRUE, repr = c("C", "R", "T"), giveCsparse) fac2Sparse(from, to = c("d", "l", "n"), drop.unused.levels = TRUE, repr = c("C", "R", "T"), giveCsparse, factorPatt12, contrasts.arg = NULL)


a sparse matrix, extending CsparseMatrix (for

fac2sparse() if repr = "C" as per default; a

TsparseMatrix or RsparseMatrix, otherwise).

For fac2Sparse(), a list of length two, both components with the corresponding transposed model matrix, where the corresponding factorPatt12 is true.

Note that model.Matrix(*, sparse=TRUE)

from package MatrixModels may be often be preferable to

sparse.model.matrix() nowadays, as model.Matrix()

returns modelMatrix

objects with additional slots assign and contrasts which relate back to the variables used.

fac2sparse(), the basic workhorse of

sparse.model.matrix(), returns the transpose

(t) of the model matrix.



an object of an appropriate class. For the default method, a model formula or terms object.


a data frame created with model.frame. If another sort of object, model.frame is called first.

for sparse.model.matrix():

A list, whose entries are contrasts suitable for input to the contrasts replacement function and whose names are the names of columns of data containing factors.

for fac2Sparse():

character string or NULL or (coercable to) "sparseMatrix", specifying the contrasts to be applied to the factor levels.


to be used as argument of model.frame if data has no "terms" attribute.


logical indicating if the transpose should be returned; if the transposed is used anyway, setting transpose = TRUE is more efficient.


should factors have unused levels dropped? The default for sparse.model.matrix has been changed to FALSE, 2010-07, for compatibility with R's standard (dense) model.matrix().


logical indicating if row names should be used.


character string passed to paste() when constructing column names from the variable name and its levels.


logical or integer indicating if (and how much) progress output should be printed.


further arguments passed to or from other methods.


(for fac2sparse():) a factor.


a character indicating the “kind” of sparse matrix to be returned. The default, "d" is for double.


deprecated, replaced with repr; logical indicating if the result must be a CsparseMatrix.


character string, one of "C", "T", or "R", specifying the sparse representation to be used for the result, i.e., one from the super classes CsparseMatrix, TsparseMatrix, or RsparseMatrix.


logical vector, say fp, of length two; when fp[1] is true, return “contrasted” t(X); when fp[2] is true, the original (“dummy”) t(X), i.e, the result of fac2sparse().


Doug Bates and Martin Maechler, with initial suggestions from Tim Hesterberg.

See Also

model.matrix in standard R's package stats.
model.Matrix which calls sparse.model.matrix or model.matrix depending on its sparse argument may be preferred to sparse.model.matrix.

as(f, "sparseMatrix") (see coerce(from = "factor", ..) in the class doc sparseMatrix) produces the transposed sparse model matrix for a single factor f (and no contrasts).


Run this code
dd <- data.frame(a = gl(3,4), b = gl(4,1,12))# balanced 2-way
options("contrasts") # the default:  "contr.treatment"
sparse.model.matrix(~ a + b, dd)
sparse.model.matrix(~ -1+ a + b, dd)# no intercept --> even sparser
sparse.model.matrix(~ a + b, dd, contrasts = list(a="contr.sum"))
sparse.model.matrix(~ a + b, dd, contrasts = list(b="contr.SAS"))

## Sparse method is equivalent to the traditional one :
stopifnot(all(sparse.model.matrix(~ a + b, dd) ==
	      Matrix(model.matrix(~ a + b, dd), sparse=TRUE)),
	  all(sparse.model.matrix(~ 0+ a + b, dd) ==
	      Matrix(model.matrix(~ 0+ a + b, dd), sparse=TRUE)))

(ff <- gl(3,4,, c("X","Y", "Z")))
fac2sparse(ff) #  3 x 12 sparse Matrix of class "dgCMatrix"
##  X  1 1 1 1 . . . . . . . .
##  Y  . . . . 1 1 1 1 . . . .
##  Z  . . . . . . . . 1 1 1 1

## can also be computed via sparse.model.matrix():
f30 <- gl(3,0    )
f12 <- gl(3,0, 12)
  all.equal(t( fac2sparse(ff) ),
	    sparse.model.matrix(~ 0+ff),
	    tolerance = 0, check.attributes=FALSE),
  is(M <- fac2sparse(f30, drop= TRUE),"CsparseMatrix"), dim(M) == c(0, 0),
  is(M <- fac2sparse(f30, drop=FALSE),"CsparseMatrix"), dim(M) == c(3, 0),
  is(M <- fac2sparse(f12, drop= TRUE),"CsparseMatrix"), dim(M) == c(0,12),
  is(M <- fac2sparse(f12, drop=FALSE),"CsparseMatrix"), dim(M) == c(3,12)

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