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From |
"Nick Cox" <n.j.cox@durham.ac.uk> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
st: RE: Re: How to eliminate the double quotes surrounding letters? |

Date |
Sat, 29 Aug 2009 16:46:40 +0100 |

Joseph gave an excellent answer. Let's fill in some of the thought processes leading to such an answer. The generic underlying question is "How do I debug my code?" and, modifying an old mathematical joke, one answer is "By staring at it until the correct code becomes obvious". We can do a little better than that as generic advice. Some basics of debugging include: 1. Read error messages really carefully. If Stata is confused -- meaning, you've confused Stata -- it may not give very informative messages, but it will do the best it can. 2. Look (again) at the code really carefully. Read from top to bottom and from left to right. 3. Try to see your code as Stata does. Empty your mind of what you want or what you mean. Stata knows _only_ what you say. Focus on: What does Stata expect here? What does Stata see here? There are other principles too, including 4. Use -trace- tools to see precisely where a program crashes. 5. Debug actively, not passively. Vary the code to see what does and doesn't work. Try simple test cases. See what data or values Stata is working with. -- but the first three, although they may look utterly obvious, get you a long way, and would have helped Rose to get (closer to) a solution. 1. Read error messages really carefully ======================================= Stata gave Rose an error message objecting to a left parenthesis "(". Rose was guessing that the double quotes in what she typed were problematic. That was not what Stata was objecting to. As it turns out, the double quotes would also have been problematic, given what Rose typed, but first things first. So, what is wrong with the "("? 2. Look (again) at the code really carefully ============================================ Stata should be thought of as like a small child learning to read. It painstakingly reads each word -- no, each character -- at a time, from top to bottom and from left to right, making tiny inferential steps one by one. (It does that really fast, but that's not the issue.) There is just one line of code here, so the left-to-right rule is the only relevant one, but it tells us something: Stata sees nothing wrong -- in terms of incorrect syntax -- with anything up to and including "subinstr", but it objects to the "(". 3. Try to see your code as Stata does ===================================== Empty your mind of what you want or what you mean. Stata knows _only_ what you say. Focus on: What does Stata expect here? What does Stata see here? Look again at the syntax for -rename-. The so-called syntax diagram is simple, and does not allow for variations: rename old_varname new_varname What does Stata expect, following the -rename- command? An old (meaning existing) varname followed by a new varname. (If you are really new to Stata, know that varname means "variable name".) Stata is expecting to see a new varname as the third element of the command, but it is seeing after macro substitution (which I won't explain here) subinstr("ab cd ef"," ","",.) Now "subinstr" could be a legal variable name, but "(" could not be part of one, so must be (part or all of) some other syntax element. But no such syntax element is allowed by the syntax, which is why Stata bails out at this point. At least, that is my reconstruction. The underlying error is that Rose wanted or expected -rename- to see the _result_ of evaluating the expression she typed that uses -subinstr()-. To get that, she must evaluate it explicitly, either in advance local newname = subinstr("`xy'", " ", "", .) rename variable `newname' or on the fly, as Joseph clearly indicates. Nick n.j.cox@durham.ac.uk Joseph Coveney ============== Use `=. . .' to evaluate the function. See example below for details. Joseph Coveney . sysuse auto (1978 Automobile Data) . keep make . local xy "ab cd ef" . rename make `=subinstr("`xy'"," ","",.)' . describe Contains data from C:\Program Files\Stata11\ado\base/a/auto.dta obs: 74 1978 Automobile Data vars: 1 13 Apr 2009 17:45 size: 1,628 (99.9% of memory free) (_dta has notes) ------------------------------------------------------------------------ -------- ------------------------ storage display value variable name type format label variable label ------------------------------------------------------------------------ -------- ------------------------ abcdef str18 %-18s Make and Model ------------------------------------------------------------------------ -------- ------------------------ Sorted by: Note: dataset has changed since last saved Rose ==== I have a localname xy containing some letters among which there is space. And I want rename a variable the localname xy. Due to the space, I took the -subinstr- funtion to eliminate the space. However, that treatment produced double-quotes surrounding the letters. How to deal with it? To make what I said clear, I take an example below. local xy "ab cd ef" rename variable subinstr("`xy'"," ","",.) Based on the typing above, Stata gives an error message "( not allowed r(101)". * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**st: How to eliminate the double quotes surrounding letters?***From:*gjhxmu@sina.com

**st: Re: How to eliminate the double quotes surrounding letters?***From:*"Joseph Coveney" <jcoveney@bigplanet.com>

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