# knn.ani: Demonstration of the k-Nearest Neighbour classification In animation: A Gallery of Animations in Statistics and Utilities to Create Animations

## Description

Demonstrate the process of k-Nearest Neighbour classification on the 2D plane.

## Usage

 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13``` ```knn.ani( train, test, cl, k = 10, interact = FALSE, tt.col = c("blue", "red"), cl.pch = seq_along(unique(cl)), dist.lty = 2, dist.col = "gray", knn.col = "green", ... ) ```

## Arguments

 `train` matrix or data frame of training set cases containing only 2 columns `test` matrix or data frame of test set cases. A vector will be interpreted as a row vector for a single case. It should also contain only 2 columns. This data set will be ignored if `interact = TRUE`; see `interact` below. `cl` factor of true classifications of training set `k` number of neighbours considered. `interact` logical. If `TRUE`, the user will have to choose a test set for himself using mouse click on the screen; otherwise compute kNN classification based on argument `test`. `tt.col` a vector of length 2 specifying the colors for the training data and test data. `cl.pch` a vector specifying symbols for each class `dist.lty, dist.col` the line type and color to annotate the distances `knn.col` the color to annotate the k-nearest neighbour points using a polygon `...` additional arguments to create the empty frame for the animation (passed to `plot.default`)

## Details

For each row of the test set, the k nearest (in Euclidean distance) training set vectors are found, and the classification is decided by majority vote, with ties broken at random. For a single test sample point, the basic steps are:

1. locate the test point

2. compute the distances between the test point and all points in the training set

3. find k shortest distances and the corresponding training set points

4. vote for the result (find the maximum in the table for the true classifications)

As there are four steps in an iteration, the total number of animation frames should be `4 * min(nrow(test), ani.options('nmax'))` at last.

## Value

A vector of class labels for the test set.

## Note

There is a special restriction (only two columns) on the training and test data set just for sake of the convenience for making a scatterplot. This is only a rough demonstration; for practical applications, please refer to existing kNN functions such as `knn` in class, etc.

If either one of `train` and `test` is missing, there'll be random matrices prepared for them. (It's the same for `cl`.)

Yihui Xie

## References

Examples at https://yihui.org/animation/example/knn-ani/

Venables, W. N. and Ripley, B. D. (2002) Modern Applied Statistics with S. Fourth edition. Springer.

`knn`