DATA MINING Desktop Survival Guide by Graham Williams
Desktop Survival Project Home List of Figures List of Tables Data Mining with Rattle Introduction Data Mining with Rattle Data Exploring Data Transforming Data Cluster Analysis Association Analysis Classification and Regression Models Evaluation and Deployment Issues Moving into R Troubleshooting R for the Data Miner R Data Graphics in R Understanding Data Preparing Data Descriptive and Predictive Analytics Issues Evaluating Models Reporting Cluster Analysis Text Mining Text Mining Algorithms Bagging Bayes Classifier Cluster Analysis Conditional Trees Hierarchical Clustering K-Nearest Neighbours Linear Models Neural Networks Support Vector Machines Open Products AlphaMiner Borgelt Data Mining Suite KNime R Rattle Weka Closed Products C4.5 Clementine Equbits Foresight GhostMiner InductionEngine ODM Enterprise Miner Statistica Data Miner TreeNet Virtual Predict Appendicies Installing GTK, R, and Rattle Glossary Bibliography Index

Building a Model

Let's have a look at the simplest of problems. Suppose we want to model one variable (e.g., a person's height) in terms of another variable (e.g., a person's age).

We can create a collection of people's ages and heights, using some totally random data:

> set.seed(123)			# To ensure repeatability.
> ages <- runif(10, 1, 20)	# Random ages between 1 and 20
> heights <- 30 + rnorm(10, 1, as.integer(ages)) + ages*5
> plot(ages, heights)

We can now build a model (in fact, a linear interpolation) that approximates this data using R's approxfun:

> my.model <- approxfun(ages, heights)
> my.model(15)
[1] 85.38172
> plot(my.model, add=TRUE, col=2, ylim=c(20,200), xlim=c(1,20))

The resulting plot is show in Figure 18.1. We can see it is only an approximate model and indeed, not a very good model. The data is pretty deficient, and we also know that generally height does not decrease for any age group in this range. It illustrates the modelling task though.

Figure 18.1: A approximate model of random data.

> my.spline <- splinefun(ages, heights)

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