Obtaining Probabilities in KNN Classifier in R - r

Question

I have the following the data set:
TRAIN dataset
Sr A B C XX
1 0.09 0.52 11.1 high
2 0.13 0.25 11.1 low
3 0.20 0.28 11.1 high
4 0.29 0.50 11.1 low
5 0.31 0.58 11.1 high
6 0.32 0.37 11.1 high
7 0.37 0.58 11.1 low
8 0.38 0.40 11.1 low
9 0.42 0.65 11.1 high
10 0.42 0.79 11.1 low
11 0.44 0.34 11.1 high
12 0.45 0.89 11.1 low
13 0.57 0.72 11.1 low
TEST dataset
Sr A B C XX
1 0.54 1.36 9.80 low
2 0.72 0.82 9.80 low
3 0.19 0.38 9.90 high
4 0.25 0.44 9.90 high
5 0.29 0.54 9.90 high
6 0.30 0.54 9.90 high
7 0.42 0.86 9.90 low
8 0.44 0.86 9.90 low
9 0.49 0.66 9.90 low
10 0.54 0.76 9.90 low
11 0.54 0.76 9.90 low
12 0.68 1.08 9.90 low
13 0.88 0.51 9.90 high
Sr : Serial Number
A-C : Parameters
XX : Output Binary Parameter
I am trying to use the KNN classifier to develop a predictor model with 5 nearest neighbors. Following is the code that I have written:
train_input <- as.matrix(train[,-ncol(train)])
train_output <- as.factor(train[,ncol(train)])
test_input <- as.matrix(test[,-ncol(test)])
prediction <- knn(train_input, test_input, train_output, k=5, prob=TRUE)
resultdf <- as.data.frame(cbind(test[,ncol(test)], prediction))
colnames(resultdf) <- c("Actual","Predicted")
RESULT dataset
A P
1 2 2
2 2 2
3 1 2
4 1 1
5 1 1
6 1 2
7 2 2
8 2 2
9 2 2
10 2 2
11 2 2
12 2 1
13 1 2
I have the following concerns:
What should I do to obtain probability values? Is this a probability of getting high or low i.e. P(high) or P(low)?
The levels are set to 1 (high) and 2 (low), which is based on the order of first appearance. If low appeared before high in the train dataset, it would have a value 1. I feel this is not good practice. Is there anyway I can avoid this?
If there were more classes (more than 2) in the classifier, how would I handle this in the classifier?
I am using the class and e1071 library.
Thanks.

Answer 1

Utility function built before the "text" argument to scan was introduced:
rd.txt <- function (txt, header = TRUE, ...)
{ tconn <- textConnection(txt)
rd <- read.table(tconn, header = header, ...)
close(tconn)
rd}
RESULT <- rd.txt(" A P
1 2 2
2 2 2
3 1 2
4 1 1
5 1 1
6 1 2
7 2 2
8 2 2
9 2 2
10 2 2
11 2 2
12 2 1
13 1 2
")
> prop.table(table(RESULT))
P
A 1 2
1 0.15385 0.23077
2 0.07692 0.53846
You can also set up prop.table to deliver row or column proportions (AKA probabilities).