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

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

Subject |
RE: st: Looping across observations (forwards and backwards) |

Date |
Tue, 4 Oct 2011 15:32:48 +0100 |

I don't fully understand what you are trying to do here, but local ++j need not stop before v_270[`j']==v_270[`i'] | v_271[`j']==v_271[`i'] and perhaps that is not guaranteed for all values of 2. so perhaps you need another condition to stop it, say that the next value of v_269 is 2. I think you need another approach. Evidently blocks start with some key values and then you count something within blocks. A few fragmentary suggestions gen start = v269 == 2 gen block = sum(start) egen start_v269 = total(start * v269), by(block) egen start_v270 = total(start * v270), by(block) egen start_v271 = total(start * v271), by(block) Nick n.j.cox@durham.ac.uk -----Original Message----- From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Pedro Nakashima Sent: 03 October 2011 20:39 To: statalist@hsphsun2.harvard.edu Subject: Re: st: Looping across observations (forwards and backwards) Thanks, Nick When I applied you tip to the code: clear all input v_269 v_270 v_271 desired_sinalt 0 1.4 100 . 1 1.5 100 . 0 1.5 95 . 0 1.4 100 . 2 1.5 100 1 1 1.7 98 . 0 1.2 99 . 2 1.5 95 -1 0 1.8 101 . end gen order = _n gen neworder=-_n sort neworder gen sinalt=. set trace on forvalues i=1/`=_N' { if v_269[`i']==2{ local j=`i'+1 while (v_270[`j']!=v_270[`i'] | v_271[`j']!=v_271[`i']) { local ++j } if v_270[`j']==v_270[`i'] | v_271[`j']==v_271[`i'] { if v_269[`j']==1{ local sinal=1 } else if v_269[`j']==0 { local sinal=-1 } else { local sinal=. } } replace sinalt=`sinal' in `i' } } set trace off sort order ,, it worked, But if I replace the third observation as follows: replace v_269 = 2 in 3 replace v_271 = 100 in 3 The looping never ends.. Also, It's important to say that if the criterion matches v_269 and v_271 in observation number 3 (where v_269==2), as in the above example, I want to ignore it. Thanks in advance for the help. Best regards Pedro Nakashima. 2011/9/24 Nick Cox <njcoxstata@gmail.com>: > A different comment is that it is much easier to go forwards in Stata > than backwards. So, reversing the whole dataset, and defining spells > "started" in a certain way might be easier. When all is done you > reverse it again. > > Reversing is easy > > gen neworder = -_n > sort neworder > > On Sat, Sep 24, 2011 at 4:07 PM, Nick Cox <njcoxstata@gmail.com> wrote: >> When your program gets to >> >> replace sinalt=`sinal' in `i' >> >> evidently `sinal' is undefined so Stata sees >> >> replace sinalt= in `i' >> >> It tries first to interpret -in- as the name of a variable or scalar, >> fails, and aborts with error. >> >> Perhaps when you coded >> >> if cod[j]==1 { >> >> you meant >> >> if cod[`j']==1 { >> >> On Sat, Sep 24, 2011 at 3:28 PM, pedromfn <nakashimapedro@gmail.com> wrote: >> >>> My database looks like: >>> >>> obs cod pr qt sinalt >>> 1 1 1.4 100 . >>> 2 2 1.5 100 . >>> 3 1 1.5 95 . >>> 4 1 1.4 100 . >>> 5 3 1.5 100 . >>> >>> and I want to replace observations of sinalt in which cod==3, according to >>> the following rule: >>> 1) Go across observations looking for observations in which cod=3 >>> 2) In the above example, the first observation is observation 5, in which >>> pr[5]=1.5 and qt[5]=100. Once that observation was found, go backwards >>> through observations looking for the first observation j in which >>> pr[j]==pr[5] & qt[j]==qt[5]. In the example, j=2. >>> 3) Replace sinalt[5]=`sinal' , where the macro sinal is defined as: >>> if cod[j]==1, store in the local sinal the value 1 >>> if cod[j]==2, store in the local sinal the value -1 >>> 4) Once last replace was done, look for the next observation in which cod==3 >>> and do the same thing. >>> >>> I wrote the following do-file, but it didn't work: >>> >>> forvalues i=1/`=_N' { >>> if cod[`i']==3{ >>> local j=`i'-1 >>> if pr[`j']==pr[`i'] & qt[`j']==qt[`i'] { >>> if cod[j]==1 { >>> local sinal 1 >>> } >>> else if cod[`j']==2 { >>> local sinal -1 >>> } >>> else { >>> local sinal >>> } >>> } >>> else { >>> while pr[`j']!=pr[`i'] | qt[`j']!=qt[`i'] { >>> local --j >>> } >>> } >>> replace sinalt=`sinal' in `i' >>> } >>> } >>> >>> ERROR: >>> in not found >>> r(111); >> > * * 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/

**Follow-Ups**:**Re: st: Looping across observations (forwards and backwards)***From:*Nick Cox <njcoxstata@gmail.com>

**References**:**Re: st: Looping across observations (forwards and backwards)***From:*Pedro Nakashima <nakashimapedro@gmail.com>

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