function preprocess () {
}
		

The JS file is organized into three separate functions: preprocess(), calculate(), and printout(). This is because not all code is needed at all stages. Currently the preprocess-function is not really used in many places (typically you will omit it altogether).

function calculate () {
	echo ('res <- t.test (x=' + getString ("x") + ', y=' + getString ("y") + ', hypothesis="' + getString ("hypothesis") + '"' + getString ("varequal"));
	var conflevel = getString ("conflevel");
	if (conflevel != "0.95") echo (', conf.level=' + conflevel);
	echo (')\n');
}
		

This function generates the actual R syntax to be run from the GUI settings. Let's look at this in detail: The code to be used is generated using echo() statement. Looking at the echo() statement step by step, the first part of it is

res <- t.test (
		

as plain text. Next we need to fill in the value, the user selected as the first variable. We fetch this using getString ("x"), and append it to the string to be “echoed”. This prints out the value of the GUI-element with id="x": our first <checkbox>. Next, we append a ', ', and do the same to fetch the value of the element "y" - the second <checkbox>. For the hypothesis (the <radio> group), and the equal variances <checkbox>, the procedure is very similar.

Note that instead of concatenating the output snippets with “+”, you can also use several echo() statements. Everything is printed on a single line. To produce a line break in the generated code, insert a "\n" in the echoed string. In theory, you can even produce many lines with a single echo-statement, but please keep it to one line (or less) of generated code per echo().

It gets a little more tricky for the confidence level. For reasons of aesthetics, we do not want to explicitly specify the confidence level to use, if it corresponds to the default value. Hence, instead of printing the value unconditionally, we first fetch into a variable. Then we check, whether that variable differs from "0.95" and if so print out an additional argument. Finally, we echo a closing bracket and a line break: ")\n". That is all for the calculate function.

function printout () {
	echo ('rk.header (' + i18n ("Two Variable t-Test") + ')\n');
	echo ('rk.print (res)\n');
}
		

And this was all there is to the printout function in most cases. rk.header() prints a standard headline for the results. Note that in the .js files, you have to mark up all translatable strings by hand, using i18n(), or some alternative commands. More on this in the chapter on internationalization. You can also add some more information to this, if you like, e.g.:

function printout () {
	new Header (i18n ("Two Variable t-Test"))
	          .addFromUI ("varequal")
	          .add (i18n ("Confidence level"), getString ("conflevel"))  // Note: written like this for illustration purposes. More automatic:
	//        .addFromUI ("conflevel")
	          .print ();
echo ('rk.print (res)\n');
}
		

rk.print() utilizes the R2HTML package to provide HTML formatted output. Another helpful function is rk.results(), which can also output different kinds of result tables. If in doubt, however, just use rk.print(), and be done with. The JS class Header is a JS level helper to generate a call to rk.header() (just take a look at the generated R code). In some cases you may want to call echo ('rk.header (...)') directly to print a header for your output.

Note that internally, the output is just a plain HTML document at this point of time. Therefore you might be tempted to add custom HTML using rk.cat.output(). While this will work, please do not do this. The output format may change (e.g. to ODF) in the future, so it is best not to introduce HTML specific code. Rather keep things simple with rk.header(), rk.print(), rk.results(), and -- if needed -- rk.print.literal(). If those do not seem to satisfy your formatting needs, contact us on the mailing list for help.

Congratulations! You created your first plugin. Read on in the next chapters for more advanced concepts.