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Re: st: Looping across observations (forwards and backwards)
From
Pedro Nakashima <[email protected]>
To
[email protected]
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 <[email protected]>:
> 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 <[email protected]> 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
>> [email protected]
>>
>> -----Original Message-----
>> From: [email protected] [mailto:[email protected]] On Behalf Of Pedro Nakashima
>> Sent: 03 October 2011 20:39
>> To: [email protected]
>> 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 <[email protected]>:
>>> 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 <[email protected]> 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 <[email protected]> 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);
>>>>
>>>
>>
>> *
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>>
>
> *
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>
*
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