I am getting attr(, nn.index) as part of my KNN output in R. What is meant by that and how is this value getting calculated?knn.pred <- knn(tdm.stack.nl_train, tdm.stack.nl_Test, tdm.cand_train)print(knn.pred)> knn.pred[1] Silent      Silent      Silent      Silent      Silent      Silent      Silent      [8] Silent      Silent      Silent    attr(,nn.index)      [,1][1,]  292  [2,]  292  [3,]  343  [4,]  444  [5,]  250  [6,]  445  [7,]  270  [8,]  228  [9,]  302  [10,]  355  
what is nn.index mean in KNN output
r;classification
I guess you are using the fnn package.attr is a list of attributes which can be used for both nn.index and nn.dist. In this case, you are using index.So, index returns an n x k matrix for the nearest neighbor indice.And the definition of the nearest neighbor index is:The nearest neighbor index is expressed as the ratio of the observed  distance divided by the expected distance.Definition reference