Notice: On April 23, 2014, Statalist moved from an email list to a forum, based at statalist.org.
| From | Bryan Sayer <bsayer@chrr.osu.edu> |
| To | statalist@hsphsun2.harvard.edu |
| Subject | Re: st: Creating a second output data set |
| Date | Fri, 09 Sep 2011 21:07:31 -0400 |
No, if you look at the bottom of the message you will see an example.The memory data set is composed of N observations. This is a probability proportional to size without replacement (stratified) sample. For the time being I am just doing one stratum at a time. See Levy and Lemeshow "Sampling of Populations" chapter 11.
Input (memory) data set (with marginal probability added) District Size pi(i) LUWEERO 12,466 0.916858 KAMPALA 3,459 0.542857 TORORO 2,815 0.448739 KAMULI 549 0.091546 Total 19,289 Output (postfile) data set: COMBINATIONS pi(I,j) LUWEERO,KAMPALA 0.468854 LUWEERO,TORORO 0.377069 LUWEERO,KAMULI 0.070934 KAMPALA,TORORO 0.062531 KAMPALA,KAMULI 0.011473 TORORO,KAMULI 0.009139 Bryan Sayer On 9/9/2011 8:13 PM, Steven Samuels wrote:
Bryan, You don't need to create any loops. I assume that the "memory" data set consists of N x (N-1)/2 observations. If you haven't done so already, create two separate variables, e.g. id_1 id__2 that uniquely identify the PSU pair. Call the joint probability j_prob. ************************** sort id_1 id_2 ************************** will give data that look like: id_1 id_2 j_prob 1 2 .07 1 3 .05 . . . N-1 N .04 Then the following code will create the data set you are requesting. ******************************************* egen marg_prog = total(j_prob), by(id_1) bys id_1: keep if _n==1 drop id_2 j_prob save ******************************************* The same procedure will work if the output data set consists of any number of tuples. For 4-tuples, for example, change the -drop- statement to: ******************** drop id_2 id_3 id_4 j_prob ***************** Out of curiosity: what selection algorithms are you studying? Steve On Sep 9, 2011, at 6:30 PM, Nick Cox wrote: Too much survey sampling in this for me to understand what you want. Someone else will probably help. On Fri, Sep 9, 2011 at 11:08 PM, Bryan Sayer<bsayer@chrr.osu.edu> wrote:Great, thanks! I tend to think more along the lines of FORTRAN. A local for the total makes sense. The total is used in the calculation of the joint probability. So locals seem to make sense for what I send to -postfile- (though I realize I probably don't have it correct yet), provided it is ok to change their value during the loops. But maybe it should be scalers? But I am still stuck on the new variable I need to add to the input data set (the one in memory). I'm going to call that "memory data set" to distinguish it from "postfile data set". The memory data set is the input for this calculation. Each observation in the memory data set is one PSU. The postfile data set consists of each possible pair of PSUs from the memory data set, thus the number of observations is the combination of _N taken 2 at a time from the memory data set (without replacement). The memory data set will gain one variable, the marginal probability (margprob ), which is the sum of the joint probabilities involving each PSU. Can I act on margprob in the memory data set one observation at a time? I presume I would generate a new variable first, assigning it a value of zero before the loops start Basically, in the loop, margprob looks like this: replace margprob[J] = margprob[J] + jointprob replace margprob[K] = margprob[K] + jointprob Where J and K are the observation number of the memory data set. Does this work? Bryan Sayer Monday to Friday, 8:30 to 5:00 Phone: (614) 442-7369 FAX: (614) 442-7329 BSayer@chrr.osu.edu On 9/9/2011 5:25 PM, Nick Cox wrote:Your code shades between Stata and incomplete Stata, as you will know. However, a key principle here is that -postfile- never sees the locals in your calling program. It just gets passed their values. That's not a problem. It's the way to get round the basic fact that one program's locals are invisible to another program. Also these two lines definitely won't work local N_total egen double `N_total'=total(`count') The first defines the local N_total as blank, which is equivalent to not defining it at all. So, Stata will read the second line as egen double = total(`count') which will fail, as no new variable name is supplied. That said, there is no need to create a variable just to hold a total. su `count', meanonly will leave r(sum) in memory and the value of that can be put somewhere appropriate, into a local or a scalar or directly into another file. On Fri, Sep 9, 2011 at 8:49 PM, Bryan Sayer<bsayer@chrr.osu.edu> wrote:So I am still a bit confused about how -postfile- works when I want to preserve the data in memory. Specifically, how I generate the variables that I want in my -postfile- output versus the new one I do want to add to the data set in memory. I'm thinking I want to use a local (maybe macro?) variable for my results that go to -postfile-? In other words, how do I distinguish variables between the two files. Also, how do I accumulate results for my new variable that goes in my memory data set. I need to accumulate a sum for two observations in memory on each post to -postfile-. Here is what I have so far, but with the last part calculating the marginal probability (note that the joint probability calculation should be on one line): program jointprob args design infile outfile psu count margprob tempvar psu1 psu2 pi_one pi_joint tempfile results /* set up the file with the joint probabilities */ postfile `results' `psu1' `psu2' using "`outfile'" ,replace /* get the number of observations and the total count */ local N=_N local N_total egen double `N_total'=total(`count') quietly { /* read the input data set and create combinations of N items taken 2 at a time, without replacement */ forvalues J = 1/`N'{ forvalues K = 1/`N'{ if `K'>`J'{ psu1=`psu'[`J'] psu2=`psu'[`K'] pi_joint=(`count[`J']'*`count[`K']'/`N_total') * ((1/(`N_total'-`count[`J']')+(1/(`N_total'-`count[`K']')) post `results' psu1 psu2 pi_joint } } } } Bryan Sayer Monday to Friday, 8:30 to 5:00 Phone: (614) 442-7369 FAX: (614) 442-7329 BSayer@chrr.osu.edu On 9/7/2011 9:44 AM, Roger Newson wrote:-postfile- will still work if there is an existing dataset in the memory. However, the new dataset will be built in a file. Best wishes Roger Roger B Newson BSc MSc DPhil Lecturer in Medical Statistics Respiratory Epidemiology and Public Health Group National Heart and Lung Institute Imperial College London Royal Brompton Campus Room 33, Emmanuel Kaye Building 1B Manresa Road London SW3 6LR UNITED KINGDOM Tel: +44 (0)20 7352 8121 ext 3381 Fax: +44 (0)20 7351 8322 Email: r.newson@imperial.ac.uk Web page: http://www.imperial.ac.uk/nhli/r.newson/ Departmental Web page: http://www1.imperial.ac.uk/medicine/about/divisions/nhli/respiration/popgenetics/reph/
Opinions expressed are those of the author, not of the institution.
On 07/09/2011 14:40, Bryan Sayer wrote:-postfile- will post my results, but my reading of how it works seems to indicate that my original data set cannot be open at the same time. The examples appear to me to clear the existing data set from memory. Admittedly, this is without me having tried anything yet, but am I not reading it correctly? What I need to do is a double loop through the input data set, outputting a record on each iteration of each loop. So I need the input data set open in memory, and a second file to post the results to. Are there any examples of something similar? Thanks! Bryan Sayer Monday to Friday, 8:30 to 5:00 Phone: (614) 442-7369 FAX: (614) 442-7329 BSayer@chrr.osu.edu On 9/6/2011 4:58 PM, Roger Newson wrote:I think you are looking for the -postfile- utility. In Stata, type help postfile to find out more. HTH. Best wishes Roger Roger B Newson BSc MSc DPhil Lecturer in Medical Statistics Respiratory Epidemiology and Public Health Group National Heart and Lung Institute Imperial College London Royal Brompton Campus Room 33, Emmanuel Kaye Building 1B Manresa Road London SW3 6LR UNITED KINGDOM Tel: +44 (0)20 7352 8121 ext 3381 Fax: +44 (0)20 7351 8322 Email: r.newson@imperial.ac.uk Web page: http://www.imperial.ac.uk/nhli/r.newson/ Departmental Web page: http://www1.imperial.ac.uk/medicine/about/divisions/nhli/respiration/popgenetics/reph/
Opinions expressed are those of the author, not of the institution.
On 06/09/2011 21:53, Bryan Sayer wrote:I need to create an output data set that will differ in the content and number of observations from the input file. The observations will be created one at a time, based on the input data set. Specifically, I am creating all combinations of N objects taken two at a time. I will probably also do permutations. The input data set (to start with) consists of N records with two variables, the primary sampling unit (PSU) and a size variable associated with the PSU (a count variable). I want to create two output data sets. One is each combination of PSU with the associated joint probability. The second has the same structure as the input data set but includes the marginal probability, calculated as the sum of the joint probabilities associated with the PSU (which are accumulated as each combination is created). The part I am stuck on is how to output the data set of combinations. Can someone point me to a program that outputs a file as calculations are made? (For those interested, this is for probability proportional to size (PPS) sampling. See, for example, Levy and Lemeshow "Sampling of Populations, chapter 11). Here is an example of one stratum: Input data set (with marginal probability added) District Size pi(i) LUWEERO 12,466 0.916858 KAMPALA 3,459 0.542857 TORORO 2,815 0.448739 KAMULI 549 0.091546 Total 19,289 Output data set: COMBINATIONS pi(I,j) LUWEERO,KAMPALA 0.468854 LUWEERO,TORORO 0.377069 LUWEERO,KAMULI 0.070934 KAMPALA,TORORO 0.062531 KAMPALA,KAMULI 0.011473 TORORO,KAMULI 0.009139
* * 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/