Cross-product with a vector

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.

y.row

A vector of same size as ind.row.

ind.row

An optional vector of the row indices that are used. If not specified, all rows are used. Don't use negative indices.

ind.col

An optional vector of the column indices that are used. If not specified, all columns are used. Don't use negative indices.

center

Vector of same length of ind.col to subtract from columns of X.

scale

Vector of same length of ind.col to divide from columns of X.

ncores

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