# rowmean: Compute column means based on a grouping variable In LTLA/TrajectoryUtils: Single-Cell Trajectory Analysis Utilities

 rowmean R Documentation

## Compute column means based on a grouping variable

### Description

Computes the column mean or median for each group of rows in a matrix.

### Usage

``````rowmean(x, group)

rowmedian(x, group)
``````

### Arguments

 `x` A numeric matrix or matrix-like object. `group` A vector or factor specifying the group assignment for each row of `x`. Alternatively, a matrix of soft assignments for each row to each group (column).

### Details

The naming scheme here is somewhat inspired by the `rowsum` function. Admittedly, it is rather confusing when `rowMeans` computes the mean for a row across all columns while `rowmean` computes the mean for a column across a subset of rows, but there you have it.

If `group` is a matrix, it is expected to contain soft assignment weights for each row in `x`. Each row of `group` should contain non-negative values that sum to unity. These are used to compute weighted means or medians via MatrixGenerics functions.

### Value

A numeric matrix with one row per level of `group`, where the value for each column contains the mean or median across the subset of rows corresponding that level.

Aaron Lun

### Examples

``````x <- matrix(runif(100), ncol = 5)
group <- sample(1:8, 20, TRUE)
(xmean <- rowmean(x, group))
(xmeds <- rowmedian(x, group))

``````

LTLA/TrajectoryUtils documentation built on Feb. 5, 2024, 11:56 a.m.