dissimilarities (version 0.3.0)

subCols: Subsetting a "dist" object by columns

Description

Efficiently extracts a column-wise subset of a "dist" object, returning the corresponding submatrix of pairwise distances. # nolint

Usage

subCols(dist, idx)

Value

A numeric "matrix" containing the pairwise distances between all rows and the specified columns.

Arguments

dist

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

idx

An integer vector, specifying the column indices of the subsetted matrix.

Author

Minh Long Nguyen

Details

This function extracts specified columns from a "dist" object without explicit conversion to a dense distance "matrix", resulting in better performance and reduced memory overhead. Particularly useful when only a subset of distances is needed for downstream tasks.

Row names are retained. If it is null, as.character(1:nObs) and as.character(idx) will be used as row and column names of the resulting matrix instead.

Examples

library("microbenchmark")
x = matrix(rnorm(200), nrow = 50)
dx = dist(x)
#Randomly subsetting a 50x10 matrix
idx = sample(1:50, 10)
microbenchmark(base::as.matrix(dx)[1:50,idx],
               proxy::as.matrix(dx)[1:50,idx],
               subCols(dx, idx))
#Check if equal
v1 = as.vector(base::as.matrix(dx)[1:50,idx])
v2 = as.vector(subCols(dx, idx))
all.equal(v1, v2)