phonTools (version 0.2-2.1)

ldclassify: Linear Discriminant Classification

Description

Classify items using linear discriminant analysis.

Usage

ldclassify (data, means, covariance, template = NULL, posterior = 'no')

Value

A vector of winning categories is returned. If winning posteriors are desired, these are returned in a second column. All posteriors are returned in separate columns for each category.

Arguments

data

A matrix in which each row represents an item to be classified, and each column represents an observation from a variable describing the item.

means

A matrix of means where each row is a mean vector specifying a candidate category. The number of columns must equal the number of columns in data.

covariance

The pooled within-groups covariance matrix to be used for classification.

template

A 'Template' object may be passed instead of a mean and covariance.

posterior

If 'winner', the posterior probability of the winning category is returned. If 'all', the posterior of every category is returned.

Author

Santiago Barreda <[e-mail]>

Details

This function classifies the items described in the data matrix by comparing them to the reference patterns for the different candidate categories represented in the means matrix. The category with the minimum Mahalanobis distance to the observed pattern (i.e., a given row of the data matrix) is selected as the winner. Mahalanobis distances are found with using the covariance matrix provided to the function.

Mean and covariance matrices can be made easily for data using the createtemplate() function included in this package.

Examples

## load Peterson & Barney vowel data
data (pb52)

## normalize vowel formant frequencies
normdvowels = normalize (pb52[,7:9], pb52$speaker, pb52$vowel)
formants = normdvowels[,1:3]
vowels = pb52$vowel

## make a vowel template based on these frequencies
template = createtemplate (formants, vowels) 

## classify vowels
answers = ldclassify (formants, template$means, template$covariance)
## compare to known categories
table (answers, vowels)