sumGroups: Group-wise sum of a matrix along one axis

In presto: Fast Functions for Differential Expression Using Wilcoxon and AUC

Group-wise sum of a matrix along one axis

Description

For each unique value of the grouping vector y, sums the corresponding rows (or columns) of X. Used internally by wilcoxauc() and collapse_counts(), but exposed as a fast group-wise reduction primitive that works on both dense matrices and dgCMatrix sparse inputs.

Usage

sumGroups(X, y, MARGIN = 2)

## S3 method for class 'dgCMatrix'
sumGroups(X, y, MARGIN = 2)

## S3 method for class 'matrix'
sumGroups(X, y, MARGIN = 2)

Arguments

X	Numeric matrix or dgCMatrix.
y	Group label vector. Coerced to integer factor codes.
MARGIN	Whether observations are along rows or columns of X. MARGIN = 2 (default): observations are rows (length(y) == nrow(X)); rows are summed within each group. MARGIN = 1: observations are columns (length(y) == ncol(X)); columns are summed within each group.

Value

Numeric matrix of shape ⁠n_groups x n_features⁠. Row order matches the integer order of factor(y).

See Also

nnzeroGroups(), wilcoxauc()

Examples

set.seed(42)
exprs <- matrix(rpois(25 * 150, lambda = 2), nrow = 25,
                dimnames = list(paste0("G", 1:25), NULL))
y <- rep(c("A", "B", "C"), each = 50)
sumGroups_res <- sumGroups(exprs, y, 1)
sumGroups_res <- sumGroups(t(exprs), y, 2)

presto documentation built on Sept. 30, 2026, 5:13 p.m.