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Create a vector, matrix or array of constants

Source: R/J.R
J.Rd

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

J(3)
#> [1] 1 1 1
J(2,3)
#>      [,1] [,2] [,3]
#> [1,]    1    1    1
#> [2,]    1    1    1
J(2,3,2)
#> , , 1
#> 
#>      [,1] [,2] [,3]
#> [1,]    1    1    1
#> [2,]    1    1    1
#> 
#> , , 2
#> 
#>      [,1] [,2] [,3]
#> [1,]    1    1    1
#> [2,]    1    1    1
#> 
J(2,3, constant=2, dimnames=list(letters[1:2], LETTERS[1:3]))
#>   A B C
#> a 2 2 2
#> b 2 2 2

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
#>       day
#>        Mon Wed Fri
#>   [1,]   3   7  11
X %*% J(3)      # row sums
#>    
#> sex [,1]
#>   M    9
#>   F   12