base (version 3.6.2)

# row: Row Indexes

## Description

Returns a matrix of integers indicating their row number in a matrix-like object, or a factor indicating the row labels.

## Usage

```row(x, as.factor = FALSE)
.row(dim)```

## Arguments

x

a matrix-like object, that is one with a two-dimensional `dim`.

dim

a matrix dimension, i.e., an integer valued numeric vector of length two (with non-negative entries).

as.factor

a logical value indicating whether the value should be returned as a factor of row labels (created if necessary) rather than as numbers.

## Value

An integer (or factor) matrix with the same dimensions as `x` and whose `ij`-th element is equal to `i` (or the `i`-th row label).

## References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.

`col` to get columns; `slice.index` for a general way to get slice indices in an array.

## Examples

Run this code
``````# NOT RUN {
x <- matrix(1:12, 3, 4)
# extract the diagonal of a matrix - more slowly than diag(x)
dx <- x[row(x) == col(x)]
dx

# create an identity 5-by-5 matrix more slowly than diag(n = 5):
x <- matrix(0, nrow = 5, ncol = 5)
x[row(x) == col(x)] <- 1
x

(i34 <- .row(3:4))
stopifnot(identical(i34, .row(c(3,4)))) # 'dim' maybe "double"
# }
``````

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