wcrossprod {car} | R Documentation

## Weighted Matrix Crossproduct

### Description

Given matrices `x` and `y` as arguments and an optional matrix or vector of weights, `w`, return a weighted matrix cross-product, `t(x) w y`. If no weights are supplied, or the weights are constant, the function uses `crossprod` for speed.

### Usage

    wcrossprod(x, y, w)

### Arguments

`x,y` | x, y numeric matrices; `missing(y)` is taken to be the same matrix as x. Vectors are promoted to single-column or single-row matrices, depending on the context.
`w` | A numeric vector or matrix of weights, conformable with `x` and `y`.

### Value

A numeric matrix, with appropriate dimnames taken from `x` and `y`.

### Author(s)

Michael Friendly, John Fox jfox@mcmaster.ca

### See Also

`crossprod`

### Examples

    set.seed(12345)
    n <- 24
    drop <- 4
    sex <- sample(c("M", "F"), n, replace=TRUE)
    x1 <- 1:n
    x2 <- sample(1:n)
    extra <- c( rep(0, n - drop), floor(15 + 10 * rnorm(drop)) )
    y1 <- x1 + 3*x2 + 6*(sex=="M") + floor(10 * rnorm(n)) + extra
    y2 <- x1 - 2*x2 - 8*(sex=="M") + floor(10 * rnorm(n)) + extra
    # assign non-zero weights to 'dropped' obs
    wt <- c(rep(1, n-drop), rep(.2,drop))

    X <- cbind(x1, x2)
    Y <- cbind(y1, y2)
    wcrossprod(X)
    wcrossprod(X, w=wt)

    wcrossprod(X, Y)
    wcrossprod(X, Y, w=wt)

    wcrossprod(x1, y1)
    wcrossprod(x1, y1, w=wt)

[Package car version 2.1-6 Index]