SOCR Data Analysis Documentation

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Revision as of 21:30, 31 July 2006

Framework and Implementation

Framework of the Analysis Component

In the "anaylsis component", there are three "sets" of classes: data, Model, and Result. They are at:

Data: edu.ucla.stat.SOCR.analysis.data.Data class.
Model Classes: under the directory of edu.ucla.stat.SOCR.analyses.model.
Result Classes: under the directory of edu.ucla.stat.SOCR.analyses.result.

Data class has a public, non-static method called "getAnalysis." This is the main and the only method you needed to implement the data analysis. It identifies the requested analysis model by taking a parameter, anaylisisType, from the caller. The legal analysis types are short primitaves defined in edu.ucla.stat.SOCR.analysis.model.AnalysisType.java. You must use those defined in this class in order for it to work. Then a model class is called by the Data class to do all the mathematical operations. All the computed results (e.g. parameter estimates and their standard error), will be put in Result class. The form of storage is by using Result's HashMap member variable (variable name is: texture). Just fetch this HashMap using "getTexture" method to get the results.

Example

Here is an example snippet. Suppose we would like to run a simple linear regression on two variables: height and weight, and the data are of the same length.


double[] heightDoubleArray = new double[] {60, 55, 51, 54, 63};
double[] weightDoubleArray = new double[] {190, 160, 110, 120, 130};
	
// you need to instantiate a data instance first.
Data testData = new Data(); 	
// submit the independent variable by appendX.
appendX("HEIGHT", heightDoubleArray, DataType.QUANTITATIVE);
// submit the independent variable by appendX.
appendY("WEIGHT", weightDoubleArray, DataType.QUANTITATIVE);	
	
// then use the following line to get the result.
try {
	Result result = data.getAnalysis(AnalysisType.SIMPLE_LINEAR_REGRESSION);
	// Result.getTexture() returns a HashMap that holds some result data.
	if (result != null) { 
		// is null if something in data goes wrong, e.g. exceptio. throwing.
		HashMap texture = result.getTexture();
		double alpha = 0, beta = 0;
		try {
		        alpha = 
                        ((Double)texture.get(SimpleLinearRegressionResult.ALPHA)).doubleValue();
		        System.out.println("alpha = " + alpha);

		} catch (NullPointerException e) {
			System.out.println("alpha could not be computed.");
		}
		try {
			beta = 
                        ((Double)texture .get(SimpleLinearRegressionResult.BETA)).doubleValue();
			System.out.println("alpha = " + alpha);
		} catch (NullPointerException e) {
			System.out.println("beta could not be computed.");
		}
	}
} catch (Exception e) {
	System.out.println("Something is wrong. No result generated.");
}

A Few Points to Note

Here are a few things you should know when you code analysis method calls:

the Exception of the outer try above consists of: DataIsEmptyException (SOCR defined), WrongAnalysisException (SOCR defined), InstantiationException, IllegalAccessException, ClassNotFoundException. What if anaysis type is not specified corretly? A WrongAnalysisException would be generated. Or, what if the array that holds data is actually null or with length zero, a DataIsEmptyException will be generated. In a public method in Data, "Exception" is thrown and that include all the above. During any of the exception situation, check exception stacks for details.

For the complete set of avaialble results, please see more examples below or check class API under edu.ucla.stat.SOCR.analsyses.example directory. All of the methods to fetch the output are under under edu.ucla.stat.SOCR.analsyses.result directory.

Data Type: Note that we have two big categories of data: QUANTITATIVE and FACTOR. For example, QUANTITATIVE can be variables like height, weight, SAT score, etc. And FACTOR can be catogorical variables such as sex(Male/Female), race(White/Black/Asian/Hispanic, etc.). The variables "QUANTITATIVE" and "FACTOR" are coded as Java constants and they are declared in DataType.java class.

A few words about addPreditor and addResponse methods: All the QUANTITATIVE varialbles must be submited in a form of int, long, float or double. All the FACTOR must be submitted in form of String. If the mapping of "QUANTITATIVE as double" and "FACTOR as String" is not used, an exception will be caused and the computation is paused. For example, if you intend to submit an array of data as QUANTITATIVE but you submit them as String, the code cannot compute for results.