dissimilarities (version 0.3.0)

subDist2Dist: Dist2Dist subsetting

Description

Efficiently extracts a subset of observations from a "dist" object and returns a new "dist" object representing only the selected distances.

Usage

subDist2Dist(dist, idx, diag = FALSE, upper = FALSE)

Value

A numeric "matrix" storing pairwise distances between the selected observations.

Arguments

dist

A "dist" object, which can be computed via the stats::dist function, representing the full pairwise distance matrix between observations.

idx

An integer vector, specifying the indices of the observations to retain.

diag

A boolean value, indicating whether to display the diagonal entries.

upper

A boolean value, indicating whether to display the upper triangular entries.

Author

Minh Long Nguyen

Details

This function subsets a "dist" object directly without explicit conversion to a dense distance "matrix". It extracts only the relevant distances corresponding to the selected indices, improving both performance and memory efficiency. The result is returned as a subsetted "dist" object, preserving compatibility with downstream functions that accept this class.

Row names are retained. If it is null, as.character(idx) will be used as row names instead.

Examples

library("microbenchmark")
x = matrix(rnorm(200), nrow = 50)
dx = dist(x)
#Subsetting the first 10 units
microbenchmark(as.dist(base::as.matrix(dx)[1:10,1:10]),
               as.dist(proxy::as.matrix(dx)[1:10,1:10]),
               subDist2Dist(dx, 1:10))
#Check if equal
v1 = as.vector(as.dist(base::as.matrix(dx)[1:10,1:10]))
v2 = as.vector(subDist2Dist(dx, 1:10))
all.equal(v1, v2)