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From |
Nick Cox <njcoxstata@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: reverse lookup |

Date |
Wed, 9 Jan 2013 03:19:18 +0000 |

The approach in my earlier code could be extended. program vallookup, sort version 8.2 syntax varname [if] [in] [, local(str) scalar(str) ] marksample touse, strok qui count if `touse' local nuse = r(N) if `nuse' == 0 error 2000 capture confirm numeric variable `varlist' if _rc == 0 { su `varlist' if `touse', meanonly if r(min) != r(max) { di as err "specification not satisfied by single value" exit 498 } di r(min) if "`local'" != "" { c_local `local' = r(min) } if "`scalar'" != "" { scalar `scalar' = r(min) } } else { sort `touse' `varlist' if `varlist'[_N - `nuse' + 1] != `varlist'[_N] { di as err "specification not satisfied by single value" exit 498 } di `varlist'[_N] if "`local'" != "" { c_local `local' = `varlist'[_N] } if "`scalar'" != "" { scalar `scalar' = `varlist'[_N] } } end On Tue, Jan 8, 2013 at 10:58 PM, Jeph Herrin <stata@spandrel.net> wrote: > String variables are a problem all their own. I usually do something like: > > encode strvar, gen(strvar_coded) > sum strvar_coded if period==1 > local rate1= /// > cond(`r(min)'==`r(max)',`=: label (strvar_coded) `=r(min)'',"") > > which however can run into trouble if there are too many values to -strvar-. > > > > On 1/8/2013 4:48 PM, Nick Cox wrote: >> >> Here's a sketch. (Also, what about string variables?) >> >> program vallookup >> version 8.2 >> syntax varname(numeric) [if] [in] [, local(str) scalar(str) ] >> >> marksample touse, strok >> qui count if `touse' >> if r(N) == 0 error 2000 >> >> capture confirm numeric variable `varlist' >> >> su `varlist' if `touse', meanonly >> if r(min) != r(max) { >> di as err "specification not satisfied by single value" >> exit 498 >> } >> >> di r(min) >> if "`local'" != "" { >> c_local `local' = r(min) >> } >> if "`scalar'" != "" { >> scalar `scalar' = r(min) >> } >> end >> >> On Tue, Jan 8, 2013 at 9:33 PM, Jeph Herrin <stata@spandrel.net> wrote: >>> >>> Yes, the Mata construct is the ideal. And obviously, one must have 1-1 >>> mapping; this I usually check by: >>> >>> sum rate if period==1 >>> local rate=cond(`r(min)'==`r(max)',r(min),.) >>> >>> I was thinking of writing some programs to do lookups like this, since I >>> have been doing so many, and thought I'd ask first for an alternative. >>> >>> thanks, >>> Jeph >>> >>> >>> On 1/8/2013 2:27 PM, Nick Cox wrote: >>>> >>>> >>>> My short answer is that yes, this is awkward, but you are working with >>>> the most obvious way to do it in Stata. The problem is that in general >>>> >>>> ... if <condition> >>>> >>>> is not guaranteed to identify precisely one observation. It might >>>> yield one, or zero or more than one. >>>> >>>> In your case you need == in your code and can use >>>> >>>> su rate if period == 1, meanonly >>>> local value = r(min) >>>> >>>> The misnamed -meanonly- is quieter and more efficient. If the >>>> condition identifies precisely one observation, then clearly r(min), >>>> r(mean), r(max) will be identical. >>>> >>>> The problem is discussed from a different angle in >>>> >>>> SJ-6-4 dm0025 . . . . . . . . . . Stata tip 36: Which observations? >>>> Erratum >>>> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . >>>> N. >>>> J. Cox >>>> Q4/06 SJ 6(4):596 (no commands) >>>> correction of example code for Stata tip 36 >>>> >>>> SJ-6-3 dm0025 . . . . . . . . . . . . . . Stata tip 36: Which >>>> observations? >>>> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . >>>> N. >>>> J. Cox >>>> Q3/06 SJ 6(3):430--432 (no >>>> commands) >>>> tip for identifying which observations satisfy some >>>> specified condition >>>> >>>> Mata is not surprisingly less awkward here: >>>> >>>> : y = 1::10 >>>> >>>> : x = runiform(10,1) >>>> >>>> : x , y >>>> 1 2 >>>> +-----------------------------+ >>>> 1 | .5044846558 1 | >>>> 2 | .0174561641 2 | >>>> 3 | .680281796 3 | >>>> 4 | .9221656218 4 | >>>> 5 | .1094441491 5 | >>>> 6 | .7122591983 6 | >>>> 7 | .765775156 7 | >>>> 8 | .0226029507 8 | >>>> 9 | .9540165765 9 | >>>> 10 | .2686450339 10 | >>>> +-----------------------------+ >>>> >>>> : select(x, y :== 1) >>>> .5044846558 >>>> >>>> Nick >>>> >>>> On Tue, Jan 8, 2013 at 7:07 PM, Jeph Herrin <stata@spandrel.net> wrote: >>>> >>>>> I've just written the same awkward code for the untoldth time, and I'm >>>>> thinking there must be a better way to do it. >>>>> >>>>> The problem is to get a particular value of a variable into a local >>>>> which >>>>> corresponds to a particular value of another variable. I think this is >>>>> usally call reverse lookup. For example, I might have -period- and >>>>> -rate- >>>>> and want to store the value of -rate- which corresponds to period = 1. >>>>> My >>>>> lazy solution is >>>>> >>>>> >>>>> sum rate if period = 1 >>>>> local rate1 `=r(mean)' >>>>> >>>>> That is, I summarize a single observation, then put the mean in local. >>>>> Is >>>>> there a better way to do this? * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: st: reverse lookup***From:*Jeph Herrin <stata@spandrel.net>

**References**:**st: reverse lookup***From:*Jeph Herrin <stata@spandrel.net>

**Re: st: reverse lookup***From:*Nick Cox <njcoxstata@gmail.com>

**Re: st: reverse lookup***From:*Jeph Herrin <stata@spandrel.net>

**Re: st: reverse lookup***From:*Nick Cox <njcoxstata@gmail.com>

**Re: st: reverse lookup***From:*Jeph Herrin <stata@spandrel.net>

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