On Mon, 3 May 2004, Giampiero Salvi wrote: > On Mon, 3 May 2004, Prof Brian Ripley wrote: > > > dist() compares pairs of rows in the x matrix. How can they have `means > > and covariances'? -- you have a sample of size one from each of two > > populations. > > > > It seems that (Gaussian) Bhattacharyya is more like mahalanobis(). > > I had planned to use mean vectors and covariance matrices I computed > over N groups of data samples as input to dist, like this > > mu_1_1 mu_1_2 ... mu_1_M cov_1_1_1 cov_1_1_2 ... cov_1_M_M > mu_2_1 mu_2_2 ... mu_2_M cov_2_1_1 cov_2_1_2 ... cov_2_M_M > ... > mu_N_1 mu_N_2 ... mu_N_M cov_N_1_1 cov_N_1_2 ... cov_N_M_M > > where N is the number of groups and M the dimension. > > I agree that it would be better to use a new function (similar to > mahalanobis), as the function dist in all the other cases uses raw > data samples, and my interpretation of the input data might be > confusing. The reason why I though of dist is that bhattacharyya is > a symmetrical distance, and the result fits well the dist class. > > One way to solve this, if you agree, would be to write a new function > bhattacharyya() that returns a dist object.
So you would be computing distances for groups of rows. That needs a different interface from dist(). -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html