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From |
Pedro Nakashima <nakashimapedro@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

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

Date |
Tue, 8 Nov 2011 19:47:18 -0200 |

Thanks Nick, but it didn't work. Below I put a larger sample , a code that worked (for this small small sample) and, at the end, a description of what I want to do. clear input v269 v270 v271 ordem novaordem sinal 1 1986 10 96 -96 . 1 1988 50 148 -148 . 1 1986 100 187 -187 . 1 1986 100 513 -513 . 1 1985 20 743 -743 . 1 1985 40 944 -944 . 1 1985 40 945 -945 . 1 1988 100 954 -954 . 2 1985 40 966 -966 1 1 1986 40 971 -971 . 1 1986 40 992 -992 . 2 1985 20 1001 -1001 1 0 1985 20 1019 -1019 . 2 1985 20 1026 -1026 -1 0 1985 40 1032 -1032 . 1 1986 100 1034 -1034 . 0 1985 40 1035 -1035 . 0 1985 40 1045 -1045 . 2 1986 10 1053 -1053 1 0 1986 40 1054 -1054 . 2 1986 100 1056 -1056 1 2 1986 40 1062 -1062 -1 2 1985 20 1064 -1064 -1 2 1985 40 1065 -1065 -1 1 1986 45 1068 -1068 . 2 1986 45 1070 -1070 1 2 1986 100 1074 -1074 1 2 1988 10 1079 -1079 0 2 1988 100 1081 -1081 1 2 1988 50 1088 -1088 1 0 1988 50 1091 -1091 . 0 1988 50 1093 -1093 . 2 1988 70 1094 -1094 0 0 1988 50 1098 -1098 . 2 1988 50 1099 -1099 -1 0 1988 10 1102 -1102 . 2 1988 10 1103 -1103 -1 0 1988 50 1104 -1104 . 2 1988 10 1105 -1105 -1 2 1988 10 1107 -1107 -1 2 1988 10 1110 -1110 -1 0 1988 50 1113 -1113 . 2 1988 50 1115 -1115 -1 2 1988 10 1116 -1116 -1 2 1988 10 1118 -1118 -1 0 1988 10 1119 -1119 . 2 1988 10 1120 -1120 -1 0 1986 40 1124 -1124 . 2 1986 10 1127 -1127 1 2 1986 10 1131 -1131 1 2 1986 10 1135 -1135 1 end sort time capture drop orde* sina* gen ordem = _n gen ordemnova = -_n sort ordemnova gen sinal2=. forvalues i=1/`=_N' { if v269[`i']==2 { local pr = v270[`i'] local qt = v271[`i'] local j=`i'+1 while ((v269[`j']==2) | (v270[`j']!=`pr' | v271[`j']!=`qt')) & (`j'<=`=_N') { local ++j } if v269[`j']==0 { local ordem = -1 } else if v269[`j']==1 { local ordem = 1 } else { local ordem = 0 } quietly replace sinal2 = `ordem' in `i' } } sort ordem Description: 1) The variable "sinal2" replicates de desired "sinal" 2) The first entry of v269 in which v269==2 has the pair v270=185 e v271=40. I want to put one of the 3 numbers (-1, 1 or 1) in the variable "sinal". What decides which one is the entry in v269 in other observation: the one that has the same values (v270==185 and v271==40). 3) To do that, I search backwards(in observations) for the pair v270==185 and v271==40, skiping observations that, even though they have the same pair v270, v271, have also v269==2. To conclude, I want to see the first observation that I find when looking backwards, starting from a observation in which v269==2, that have either v269==0 or v269==1 4) For the first case in which v269==2 occurs, the looping go backwards 2 observations (2 observations before we have v269==1, v270==185 and v271==40). Seeing this v269==1, I store the value +1 in the local macro "ordem" and then put it in variable sinal. For the second case in which v269==2 occurs, the looping go backwards 7 observations . For the third case, the looping go backwards 2 observations. And so on.. The problem is that when running this code in a dta-file that has 920,000 lines, time goes by and it seems the task will never end. And I think it's not normal. I wonder if a code without loopings, as you did first, would be able to do what I described, given that It's perfect possible 1) that we can have consecutive observations v269==2 and, 2) the number of times the macro j is increased can overlap among v269==2 observations. I would thank if one could think with me of this problem. Also it might be usefull for other people.. Best, Pedro. 2011/10/4 Nick Cox <njcoxstata@gmail.com>: > I have looked at this again. I am still not sure what you are trying > to do here, but this reproduces your first example: > > 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 long order = _n > gen start = v_269 == 2 > gen block = sum(start) > bysort block (order) : /// > gen match = sum(v_270 == v_270[1] | v_271 == v_271[1]) > by block : /// > replace match = sum(cond(inlist(v_269, 1, 0), v_269 * (match == 1),.)) > by block : replace match = match[_N] > by block : gen sinalt = cond(match == 1, 1, cond(match == 0, -1, .)) if block > > > > > On Tue, Oct 4, 2011 at 3:32 PM, Nick Cox <n.j.cox@durham.ac.uk> wrote: >> 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/ >> > > * > * 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/ > * * 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/

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