Product with a vector — big_prodVec • bigstatsr

Product between a Filebacked Big Matrix and a vector.

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

Arguments

X: An object of class FBM.
y.col: A vector of same size as ind.col.
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

\(X \cdot y\).

Examples

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

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