[U] User's Guide

94 [ U ] 11 Language syntaxTechnical noteOnce you have typed the varlist for the command, you can place options anywhere in the command.You can type summarize marriage rate divorce rate if region=="West", detail, or youcan type summarize marriage rate divorce rate, detail, if region=="West". You use asecond comma to indicate a return to the command line as opposed to the option list. Leaving outthe comma after the word detail would cause an error because Stata would attempt to interpret thephrase if region=="West" as an option rather than as part of the command.You may not type an option in the middle of a varlist. Typing summarize marriage rate,detail, divorce rate will result in an error.Options need not be specified contiguously. You may type summarize marriage rate divorcerate, detail, if region=="South", noformat. Both detail and noformat are options.Technical noteMost options are toggles—they indicate that something either is or is not to be done. Sometimesit is difficult to remember which is the default. The following rule applies to all options: if optionis an option, then nooption is an option as well, and vice versa. Thus if we could not rememberwhether detail or nodetail were the default for summarize but we knew that we did not wantthe detail, we could type summarize, nodetail. Typing the nodetail option is unnecessary, butStata will not complain.Some options take arguments. The Stata kdensity command has an n(#) option that indicatesthe number of points at which the density estimate is to be evaluated. When an option takes anargument, the argument is enclosed in parentheses.Some options take more than one argument. In such cases, arguments should be separated fromone another by commas. For instance, you might see in a syntax diagramsaving(filename [ , replace ] )Here replace is the (optional) second argument. Lists, such as lists of variables (varlists) and listsof numbers (numlists), are considered to be one argument. If a syntax diagram reportedpowers(numlist)the list of numbers would be one argument, so the elements would not be separated by commas. Youwould type, for instance, powers(1 2 3 4). In fact, Stata will tolerate commas here, so you couldtype powers(1,2,3,4).Some options take string arguments. regress has an eform() option that works this way—forinstance, eform("Exp Beta"). To play it safe, you should type the quotes surrounding the string,although it is not required. If you do not type the quotes, any sequence of two or more consecutiveblanks will be interpreted as one blank. Thus eform(Exp beta) would be interpreted the same aseform(Exp beta).