Re: st: Wishlist for Stata 13 - index()

["Li Chuntao (Tony)" <leechtcn@gmail.com>]

Thanks Alan, it is clear with your detailed explaination. You are
really helpful!

Cheers

Chuntao



On Thu, Jun 6, 2013 at 1:09 PM, Alan Riley <ariley@stata.com> wrote:
> Chuntao (leechtcn@gmail.com) is concerned that Stata may drop the
> -index()- function.  He also finds the -indexnot()- function to be
> a bit confusing:
>
>> The string function index(s1,s2) is quite useful and still usable in
>> Stata12, which returns the position of the first character of s2 if it
>> can be found in s1, and zero otherwise. Unfortunately, this function
>> is no longer listed in manual and her helps are also missing. New
>> users have to use indexnot(), which is not straight forwardly defined
>> and many user may find it quite strang.
>>
>> Following is the output of some indexnot() and i actually totally lost
>> with them;
>>
>> . di indexnot("d", "abcdefg")
>> 0
>> . di indexnot("abcdefg", "a")
>> 2
>> . di indexnot("abcdefg", "c")
>> 1
>> . di indexnot("abcdefg", "d")
>> 1
>> . di indexnot("abcdefg", "s")
>> 1
>> . di indexnot("d", "abcdefg")
>> 0
>> . di indexnot("a", "abcdefg")
>> 0
>> I suggest Stata 13 to keep the index() function, if do not want to
>> drop indexnot()
>
> First, let me assure Chuntao that the functionality provided by
> -index()- will not go away.  In Stata 9, the -index()- function
> was renamed to -strpos()-.  So, to find help for it now, Chuntao
> can type -help strpos()-.  Both -index()- and -strpos()- exist
> in Stata 12 and do the same thing.
>
> By the way, now is a good time to point out that if you know the name of
> a Stata function (as opposed to a Stata command), the proper way to view
> the help file for it is to include the parentheses after the function
> name when you type -help-:
>
>    . help index()
>
>    . help strpos()
>
> Because Chuntao expressed some confusion about the -indexnot()-
> function, I will also try to explain how it works.  It takes
> two arguments.  The first -- let's call it "s1" -- is a string
> to be searched.  The second -- let's call it "s2" is a set of
> individual characters to search for within s1.  -indexnot()-
> returns the index within s1 of the first character NOT in s2.
>
> Here are a few examples that Chuntao tried, along with an explanation
> for each:
>
>    . display indexnot("d", "abcdefg")
>
>      s1 is "d".  s2 is the set of characters "abcdefg".  Notice that
>      "d" is one of the characters in s2.  Given that, what is the position
>      of the first character in s1 not found in s2?  Well, there isn't
>      one, because "d" is in s2, and "d" is found in s1.  So, -indexnot()
>      returns 0.
>
>    . display indexnot("abcdefg", "a")
>
>      s1 is "abcdefg" and s2 contains only 1 character, "a".  The first
>      position within s1 where a character from s2 is not found is "2",
>      which is what indexnot() returns.  "a" is found as the first character
>      in s1, but the second character in s1, "b", is not among the
>      characters listed in s2, so "2" is the value returned.
>
>    . display indexnot("abcdefg", "c")
>
>      s1 is again "abcdefg", and s2 is the single character "c".  The first
>      character in s1 that is not also in s2 is the very first character of
>      s1, "a".  So, the value returned by -indexnot()- is 1.
>
> I hope this makes -indexnot()- a little more clear.
>
>
> Alan
> ariley@stata.com
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