Cross-product between a Filebacked Big Matrix and a vector.

big_cprodVec(
X,
y.row,
ind.row = rows_along(X),
ind.col = cols_along(X),
center = NULL,
scale = NULL,
ncores = 1
)

## Arguments

X An object of class FBM. A vector of same size as ind.row. An optional vector of the row indices that are used. If not specified, all rows are used. Don't use negative indices. An optional vector of the column indices that are used. If not specified, all columns are used. Don't use negative indices. Vector of same length of ind.col to subtract from columns of X. Vector of same length of ind.col to divide from columns of X. Number of cores used. Default doesn't use parallelism. You may use nb_cores.

## Value

$$X^T \cdot y$$.

## Examples

X <- big_attachExtdata()
n <- nrow(X)
m <- ncol(X)
y <- rnorm(n)

test <- big_cprodVec(X, y)             # vector
true <- crossprod(X[], y)  # one-column matrix
all.equal(test, as.numeric(true))
#> [1] TRUE
# subsetting
ind.row <- sample(n, n/2)
ind.col <- sample(m, m/2)

tryCatch(test2 <- big_cprodVec(X, y, ind.row, ind.col),
error = function(e) print(e))
#> <simpleError: Incompatibility between dimensions.
#> 'y.row' and 'ind.row' should have the same length.># returns an error. You need to use the subset of y:
test2 <- big_cprodVec(X, y[ind.row], ind.row, ind.col)
true2 <- crossprod(X[ind.row, ind.col], y[ind.row])
all.equal(test2, as.numeric(true2))
#> [1] TRUE