# J

From matlib v0.9.2
by Michael Friendly

##### Create a vector, matrix or array of constants

This function creates a vector, matrix or array of constants, typically used for the unit vector or unit matrix in matrix expressions.

##### Usage

`J(..., constant = 1, dimnames = NULL)`

##### Arguments

- ...
One or more arguments supplying the dimensions of the array, all non-negative integers

- constant
The value of the constant used in the array

- dimnames
Either

`NULL`

or the names for the dimensions.

##### Details

The `"dimnames"`

attribute is optional: if present it is a list with one component for each dimension,
either `NULL`

or a character vector of the length given by the element of the `"dim"`

attribute for that
dimension. The list can be named, and the list names will be used as names for the dimensions.

##### Examples

```
# NOT RUN {
J(3)
J(2,3)
J(2,3,2)
J(2,3, constant=2, dimnames=list(letters[1:2], LETTERS[1:3]))
X <- matrix(1:6, nrow=2, ncol=3)
dimnames(X) <- list(sex=c("M", "F"), day=c("Mon", "Wed", "Fri"))
J(2) %*% X # column sums
X %*% J(3) # row sums
# }
```

*Documentation reproduced from package matlib, version 0.9.2, License: GPL (>= 2)*

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