# sparseNAMatrix-class

From recommenderlab v0.2-1
by Michael Hahsler

Sparse Matrix Representation With NAs Not Explicitly Stored

Coerce from and to a
sparse matrix representation where `NA`

s are not explicitly stored.

##### Usage

```
dropNA(x)
dropNA2matrix(x)
```

##### Arguments

- x
- a matrix (for
`dropNA()`

). A sparse matrix (for`dropNA2matrix()`

)

##### Details

The representation is based on
the sparse dgCMatrix in Matrix but instead of zeros, `NA`

s are dropped.

**Note:** Be careful when working with matrix operations
(multiplication, addition, etc.) since these will use the dgCMatrix superclass
which assumes that all dropped values are zero and not NA!
This means that the operations might remove zeros or add to NAs incorrectly.

##### Value

- Returns a dgCMatrix or a matrix, respectively.

##### See Also

`dgCMatrix`

in Matrix.

##### Examples

```
m <- matrix(sample(c(NA,0:5),50, replace=TRUE, prob=c(.5,rep(.5/6,6))),
nrow=5, ncol=10, dimnames = list(users=paste('u', 1:5, sep=''),
items=paste('i', 1:10, sep='')))
m
## drop all NAs in the representation
sparse <- dropNA(m)
sparse
## convert back to matrix
dropNA2matrix(sparse)
```

*Documentation reproduced from package recommenderlab, version 0.2-1, License: GPL-2*

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