nnzero The Number of Non-Zero Values of a Matrix

Description

Returns the number of non-zero values of a numeric-like R object, and in particular an object x inheriting from class Matrix.

Usage

nnzero(x, na.counted = NA)

Arguments

x

an R object, typically inheriting from class Matrix or numeric.

na.counted

a logical describing how NAs should be counted. There are three possible settings for na.counted: TRUE NAs are counted as non-zero (since “they are not zero”). NA (default)the result will be NA if there are NA's in x (since “NA's are not known, i.e., may be zero”). FALSE NAs are omitted from x before the non-zero entries are counted. For sparse matrices, you may often want to use na.counted = TRUE.

Value

the number of non zero entries in x (typically integer).

Note that for a symmetric sparse matrix S (i.e., inheriting from class symmetricMatrix), nnzero(S) is typically twice the length(S@x).

Methods

signature(x = "ANY")

the default method for non-Matrix class objects, simply counts the number 0s in x, counting NA's depending on the na.counted argument, see above.

signature(x = "denseMatrix")

conceptually the same as for traditional matrix objects, care has to be taken for "symmetricMatrix" objects.

signature(x = "diagonalMatrix"), and signature(x = "indMatrix")

fast simple methods for these special "sparseMatrix" classes.

signature(x = "sparseMatrix")

typically, the most interesting method, also carefully taking "symmetricMatrix" objects into account.

See Also

The Matrix class also has a length method; typically, length(M) is much larger than nnzero(M) for a sparse matrix M, and the latter is a better indication of the size of M.

drop0, zapsmall.

Examples

m <- Matrix(0+1:28, nrow = 4)
m[-3,c(2,4:5,7)] <- m[ 3, 1:4] <- m[1:3, 6] <- 0
(mT <- as(m, "dgTMatrix"))
nnzero(mT)
(S <- crossprod(mT))
nnzero(S)
str(S) # slots are smaller than nnzero()
stopifnot(nnzero(S) == sum(as.matrix(S) != 0))# failed earlier

data(KNex)
M <- KNex$mm
class(M)
dim(M)
length(M); stopifnot(length(M) == prod(dim(M)))
nnzero(M) # more relevant than length
## the above are also visible from
str(M)