csi: Cosine Similarity Index

Description Usage Arguments Value Note Author(s) Examples

View source: R/csi.R

Description

Calculates the cosine similarity and angular similarity on two vectors or a matrix

Usage

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csi(x, y = NULL)

Arguments

x

A vector or matrix object

y

If x is a vector, then a vector object

Value

If x is a matrix, a list object with: similarity and angular.similarity matrices

If x and y are vectors, a vector of similarity and angular.similarity

Note

The cosine similarity index is a measure of similarity between two vectors of an inner product space. This index is bested suited for high-dimensional positive variable space. One useful application of the index is to measure separability of clusters derived from algorithmic approaches (e.g., k-means). It is a good common practice to centre the data before calculating the index. It should be noted that the cosine similarity index is mathematically, and often numerically, equivalent to the Pearson's correlation coefficient

cosine similarity index is derived:

s(xy) = x * y / ||x|| * ||y||

expected 1.0 (perfect similarity) to -1.0 (perfect dissimilarity)

A normalised angle between the vectors can be used as a bounded similarity function within [0,1]

angular similarity = 1 - (cos(s)^-1/pi)

Author(s)

Jeffrey S. Evans <[email protected]>

Examples

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# Compare two vectors (centred using scale)
  x=runif(100)
  y=runif(100)^2
  csi(as.vector(scale(x)),as.vector(scale(y)))
  
  #' # Compare columns (vectors) in a matrix (centred using scale)
  x <- matrix(round(runif(100),0),nrow=20,ncol=5)
  ( s <- csi(scale(x)) )
    
# Compare vector (x) to each column in a matrix (y)
y <- matrix(round(runif(500),3),nrow=100,ncol=5)
x=runif(100) 
csi(as.vector(scale(x)),scale(y))

jeffreyevans/spatialEco documentation built on Nov. 10, 2018, 4:13 a.m.