1 Peter Fox Data Analytics – ITWS-4963/ITWS-6965 Week 5a, February 24, 2015 Weighted kNN, ~ clustering, trees and Bayesian classification

Plot tools/ tips r/ pairs, gpairs, scatterplot.matrix, clustergram, etc. data() # precip, presidents, iris, swiss, sunspot.month (!), environmental, ethanol, ionosphere More script fragments in R will be available on the web site ( ) 2

Weighted KNN? require(kknn) data(iris) m <- dim(iris)[1] val <- sample(1:m, size = round(m/3), replace = FALSE, prob = rep(1/m, m)) iris.learn <- iris[-val,] iris.valid <- iris[val,] iris.kknn <- kknn(Species~., iris.learn, iris.valid, distance = 1, kernel = "triangular") summary(iris.kknn) fit <- fitted(iris.kknn) table(iris.valid$Species, fit) pcol <- as.character(as.numeric(iris.valid$Species)) pairs(iris.valid[1:4], pch = pcol, col = c("green3", "red”)[(iris.valid$Species != fit)+1]) 3

4 Look at Lab5b_wknn_2015.R

Ctree > iris_ctree <- ctree(Species ~ Sepal.Length + Sepal.Width + Petal.Length + Petal.Width, data=iris) > print(iris_ctree) Conditional inference tree with 4 terminal nodes Response: Species Inputs: Sepal.Length, Sepal.Width, Petal.Length, Petal.Width Number of observations: 150 1) Petal.Length <= 1.9; criterion = 1, statistic = )* weights = 50 1) Petal.Length > 1.9 3) Petal.Width <= 1.7; criterion = 1, statistic = ) Petal.Length <= 4.8; criterion = 0.999, statistic = )* weights = 46 4) Petal.Length > 4.8 6)* weights = 8 3) Petal.Width > 1.7 7)* weights = 46 5

plot(iris_ctree) 6 Try Lab6b_5_2014.R > plot(iris_ctree, type="simple”) # try this

Swiss - pairs 7 pairs(~ Fertility + Education + Catholic, data = swiss, subset = Education < 20, main = "Swiss data, Education < 20")

New dataset - ionosphere require(kknn) data(ionosphere) ionosphere.learn <- ionosphere[1:200,] ionosphere.valid <- ionosphere[-c(1:200),] fit.kknn <- kknn(class ~., ionosphere.learn, ionosphere.valid) table(ionosphere.valid$class, fit.kknn$fit) # vary kernel (fit.train1 <- train.kknn(class ~., ionosphere.learn, kmax = 15, kernel = c("triangular", "rectangular", "epanechnikov", "optimal"), distance = 1)) table(predict(fit.train1, ionosphere.valid), ionosphere.valid$class) #alter distance (fit.train2 <- train.kknn(class ~., ionosphere.learn, kmax = 15, kernel = c("triangular", "rectangular", "epanechnikov", "optimal"), distance = 2)) table(predict(fit.train2, ionosphere.valid), ionosphere.valid$class) 8

Results ionosphere.learn <- ionosphere[1:200,] # convenience samping!!!! ionosphere.valid <- ionosphere[-c(1:200),] fit.kknn <- kknn(class ~., ionosphere.learn, ionosphere.valid) table(ionosphere.valid$class, fit.kknn$fit) b g b 19 8 g

(fit.train1 <- train.kknn(class ~., ionosphere.learn, kmax = 15, + kernel = c("triangular", "rectangular", "epanechnikov", "optimal"), distance = 1)) Call: train.kknn(formula = class ~., data = ionosphere.learn, kmax = 15, distance = 1, kernel = c("triangular", "rectangular", "epanechnikov", "optimal")) Type of response variable: nominal Minimal misclassification: 0.12 Best kernel: rectangular Best k: 2 table(predict(fit.train1, ionosphere.valid), ionosphere.valid$class) b g b 25 4 g

(fit.train2 <- train.kknn(class ~., ionosphere.learn, kmax = 15, + kernel = c("triangular", "rectangular", "epanechnikov", "optimal"), distance = 2)) Call: train.kknn(formula = class ~., data = ionosphere.learn, kmax = 15, distance = 2, kernel = c("triangular", "rectangular", "epanechnikov", "optimal")) Type of response variable: nominal Minimal misclassification: 0.12 Best kernel: rectangular Best k: 2 table(predict(fit.train2, ionosphere.valid), ionosphere.valid$class) b g b 20 5 g

However… there is more 12

Bayes > cl <- kmeans(iris[,1:4], 3) > table(cl$cluster, iris[,5]) setosa versicolor virginica # > m <- naiveBayes(iris[,1:4], iris[,5]) > table(predict(m, iris[,1:4]), iris[,5]) setosa versicolor virginica setosa versicolor virginica pairs(iris[1:4],main="Iris Data (red=setosa,green=versicolor,blue=virginica)", pch=21, bg=c("red","green3","blue")[u nclass(iris$Species)])

Using a contingency table > data(Titanic) > mdl <- naiveBayes(Survived ~., data = Titanic) > mdl 14 Naive Bayes Classifier for Discrete Predictors Call: naiveBayes.formula(formula = Survived ~., data = Titanic) A-priori probabilities: Survived No Yes Conditional probabilities: Class Survived 1st 2nd 3rd Crew No Yes Sex Survived Male Female No Yes Age Survived Child Adult No Yes

Using a contingency table > predict(mdl, as.data.frame(Titanic)[,1:3]) [1] Yes No No No Yes Yes Yes Yes No No No No Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes No [26] No No No Yes Yes Yes Yes Levels: No Yes 15

Naïve Bayes – what is it? Example: testing for a specific item of knowledge that 1% of the population has been informed of (don’t ask how). An imperfect test: –99% of knowledgeable people test positive –99% of ignorant people test negative If a person tests positive – what is the probability that they know the fact? 16

Naïve approach… We have 10,000 representative people 100 know the fact/item, 9,900 do not We test them all: –Get 99 knowing people testing knowing –Get 99 not knowing people testing not knowing –But 99 not knowing people testing as knowing Testing positive (knowing) – equally likely to know or not = 50% 17

Tree diagram ppl 1% know (100ppl) 99% test to know (99ppl) 1% test not to know (1per) 99% do not know (9900ppl) 1% test to know (99ppl) 99% test not to know (9801ppl) 18

Relation between probabilities For outcomes x and y there are probabilities of p(x) and p (y) that either happened If there’s a connection then the joint probability - both happen = p(x,y) Or x happens given y happens = p(x|y) or vice versa then: –p(x|y)*p(y)=p(x,y)=p(y|x)*p(x) So p(y|x)=p(x|y)*p(y)/p(x) (Bayes’ Law) E.g. p(know|+ve)=p(+ve|know)*p(know)/p(+ve)= (.99*.01)/(.99* *.99) =

How do you use it? If the population contains x what is the chance that y is true? p(SPAM|word)=p(word|SPAM)*p(SPAM)/p(w ord) Base this on data: –p(spam) counts proportion of spam versus not –p(word|spam) counts prevalence of spam containing the ‘word’ –p(word|!spam) counts prevalence of non-spam containing the ‘word’ 20

Or.. What is the probability that you are in one class (i) over another class (j) given another factor (X)? Invoke Bayes: Maximize p(X|Ci)p(Ci)/p(X) (p(X)~constant and p(Ci) are equal if not known) So: conditional indep - 21

P(x k | C i ) is estimated from the training samples – Categorical: Estimate P(x k | C i ) as percentage of samples of class i with value x k Training involves counting percentage of occurrence of each possible value for each class –Numeric: Actual form of density function is generally not known, so “normal” density is often assumed 22

Digging into iris classifier<-naiveBayes(iris[,1:4], iris[,5]) table(predict(classifier, iris[,-5]), iris[,5], dnn=list('predicted','actual')) classifier$apriori classifier$tables$Petal.Length plot(function(x) dnorm(x, 1.462, ), 0, 8, col="red", main="Petal length distribution for the 3 different species") curve(dnorm(x, 4.260, ), add=TRUE, col="blue") curve(dnorm(x, 5.552, ), add=TRUE, col = "green") 23

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Decision tree (example) > require(party) # don’t get me started! > str(iris) 'data.frame':150 obs. of 5 variables: $ Sepal.Length: num $ Sepal.Width : num $ Petal.Length: num $ Petal.Width : num $ Species : Factor w/ 3 levels "setosa","versicolor",..: > iris_ctree <- ctree(Species ~ Sepal.Length + Sepal.Width + Petal.Length + Petal.Width, data=iris) 25

plot(iris_ctree) 26 Try Lab6b_5_2014.R > plot(iris_ctree, type="simple”) # try this

Beyond plot: pairs pairs(iris[1:4], main = "Anderson's Iris Data -- 3 species”, pch = 21, bg = c("red", "green3", "blue")[unclass(iris$Species)]) 27 Try Lab6b_2_2014.R - USJudgeRatings

Try hclust for iris 28

gpairs(iris) 29 Try Lab6b_3_2014.R

Better scatterplots 30 install.packages("car") require(car) scatterplotMatrix(iris) Try Lab6b_4_2014.R

splom(iris) # default 31 Try Lab6b_7_2014.R

splom extra! require(lattice) super.sym <- trellis.par.get("superpose.symbol") splom(~iris[1:4], groups = Species, data = iris, panel = panel.superpose, key = list(title = "Three Varieties of Iris", columns = 3, points = list(pch = super.sym$pch[1:3], col = super.sym$col[1:3]), text = list(c("Setosa", "Versicolor", "Virginica")))) splom(~iris[1:3]|Species, data = iris, layout=c(2,2), pscales = 0, varnames = c("Sepal\nLength", "Sepal\nWidth", "Petal\nLength"), page = function(...) { ltext(x = seq(.6,.8, length.out = 4), y = seq(.9,.6, length.out = 4), labels = c("Three", "Varieties", "of", "Iris"), cex = 2) }) parallelplot(~iris[1:4] | Species, iris) parallelplot(~iris[1:4], iris, groups = Species, horizontal.axis = FALSE, scales = list(x = list(rot = 90))) > Lab6b_7_2014.R 32

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Using a contingency table > data(Titanic) > mdl <- naiveBayes(Survived ~., data = Titanic) > mdl 35 Naive Bayes Classifier for Discrete Predictors Call: naiveBayes.formula(formula = Survived ~., data = Titanic) A-priori probabilities: Survived No Yes Conditional probabilities: Class Survived 1st 2nd 3rd Crew No Yes Sex Survived Male Female No Yes Age Survived Child Adult No Yes Try Lab6b_9_2014.R

ench/html/HouseVotes84.html require(mlbench) data(HouseVotes84) model <- naiveBayes(Class ~., data = HouseVotes84) predict(model, HouseVotes84[1:10,-1]) predict(model, HouseVotes84[1:10,-1], type = "raw") pred <- predict(model, HouseVotes84[,-1]) table(pred, HouseVotes84$Class) 36

Exercise for you > data(HairEyeColor) > mosaicplot(HairEyeColor) > margin.table(HairEyeColor,3) Sex Male Female > margin.table(HairEyeColor,c(1,3)) Sex Hair Male Female Black Brown Red Blond How would you construct a naïve Bayes classifier and test it? 37

Hierarchical clustering > d <- dist(as.matrix(mtcars)) > hc <- hclust(d) > plot(hc) 38

ctree 39 require(party) swiss_ctree <- ctree(Fertility ~ Agriculture + Education + Catholic, data = swiss) plot(swiss_ctree)

Hierarchical clustering 40 > dswiss <- dist(as.matrix(swiss)) > hs <- hclust(dswiss) > plot(hs)

scatterplotMatrix 41

require(lattice); splom(swiss) 42

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At this point… You may realize the inter-relation among classification at an absolute and relative level (i.e. hierarchical -> trees…) –Trees are interesting from a decision perspective: if this or that, then this…. Beyond just distance measures (kmeans) to probabilities (Bayesian) So many ways to visualize them… 45