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

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

Subject |
RE: st: RE: combining frequency tables |

Date |
Wed, 25 Feb 2009 11:16:23 -0000 |

I wasn't paying attention to the implications of the fact that you were doing this under -by:-, but a very little experimentation and analysis is enough to clarify what is happening. Your speculation is the wrong way round. It's not a question of what -matrix- will "accept"; if there were a problem with that there would be an error message. It's a question of what is left behind earlier that -matrix- can get hold of. Forget Rose Ann Medeiros' -mdesc- and my hack -mmdesc- and focus on something accessible to all. . sysuse auto (1978 Automobile Data) . bysort foreign : su mpg ------------------------------------------------------------------------ --------- -> foreign = Domestic Variable | Obs Mean Std. Dev. Min Max -------------+-------------------------------------------------------- mpg | 52 19.82692 4.743297 12 34 ------------------------------------------------------------------------ ------- -> foreign = Foreign Variable | Obs Mean Std. Dev. Min Max -------------+-------------------------------------------------------- mpg | 22 24.77273 6.611187 14 41 . ret li scalars: r(N) = 22 r(sum_w) = 22 r(mean) = 24.77272727272727 r(Var) = 43.70779220779221 r(sd) = 6.611186898567625 r(min) = 14 r(max) = 41 r(sum) = 545 This is typical (although not universal) of how -by:- works with r-class results. What happens is that 1. -summarize- does the work for Domestic cars, showing the results and leaving them in r-class results, such as r(N), r(mean), etc. 2. -summarize- does the work for Foreign cars, showing the results and leaving them in r-class results, such as r(N), r(mean), etc. What's left behind -- and what you can access therefore -- is just the _last_ set of r-class results. As it goes through the subsets, Stata overwrites each set of r-class results with the next. This is generic of byable commands (in Stata's jargon) written as -recall- commands not -onecall- commands. Look at the code for -mdesc- and -mmdesc- and you will see that they are -recall- commands. What's to be done? Here are three solutions; there are probably others too. 1. Rewrite -mdesc- or -mmdesc- to be -onecall- commands. That's a job for a Stata programmer. 2. Use -statsby-, say with -mdesc-. (If you don't know about -statsby-, find out anyway.) 3. Call -mmdesc- in a loop and accumulate results. There's more on technique at FAQ . . . . . . . . . . Making foreach go through all values of a variable 8/05 Is there a way to tell Stata to try all values of a particular variable in a foreach statement without specifying them? http://www.stata.com/support/faqs/data/foreach.html This could be something like egen which = group(treatment timpoint), label su which, meanonly local ng = r(max) forval i = 1/`ng' { di "`: label (group) `i''" mmdesc use1 use2 matrix all = nullmat(all) \ r(table) } I am not paying attention to your extra -if- conditions which impart another level of complexity. You would need to call -mmdesc- for each distinct set of conditions. After each call to -mmdesc- you would need to copy the resulting matrix before it was overwritten. Nick n.j.cox@durham.ac.uk Shehzad Ali Thanks, Nick. For some reason, I am having no joy using the -mat- option. This may be because I am using -by- option with -mmdes- and -mat- is not willing to accept (at least in my case) multiple rows that represented different -by- categories. I am still getting a single row matrix even for the first step before I join two matrices. I think I will do this in Excel. On Feb 23 2009, Nick Cox wrote: >-findit mdesc- reveals that it is >a program by Rose Anne Medeiros, who once wrote a program called -njc-, >for which I am not responsible. Here is a matrix version of her program, >for which she is not responsible. > >*! mmdesc 1.0 NJC 23 February 2009 >* mdesc 1.0 RAM 18 JULY 2008 >* Returns a table with number missing, total, and missing/total >program mmdesc, rclass byable(recall) >version 8 >syntax [varlist] [if] [in] >tempvar touse >mark `touse' `if' `in' >local nvars : word count `varlist' >tempname matrix >matrix `matrix' = J(`nvars', 3, .) >local i = 1 >quietly foreach var of local varlist { > count if missing(`var') & `touse' > matrix `matrix'[`i', 1] = r(N) > count if `touse' > matrix `matrix'[`i', 2] = r(N) > matrix `matrix'[`i', 3] = `matrix'[`i',1] / `matrix'[`i',2] > local ++i >} >matrix rownames `matrix' = `varlist' >matrix colnames `matrix' = Missing Total Missing/Total >matrix list `matrix', noheader >return matrix table = `matrix' >end > >Once you run this, you can save its results by e.g. > >mat A = r(table) > >... > >mat B = r(table) > >... > >mat C = A + B > > >Nick >n.j.cox@durham.ac.uk > >Shehzad Ali > >Another (perhaps) simple question: is it possible to add different >frequency tables together to form a combined single table in Excel? > >I have two group variables (say, var1: type of treatment; and var2: time > >point of observation) and 5 use variables. So an observation would be >for >treatment A at time point 1. I want to know the number of missing values > >for each use variable for each treatment group and each time point. Also > >for each use variable there are 'if' conditions, so I can't do the >frequency count in one go. Here is what I am doing using a user written >programme -mdesc- or -missing-: > >by treatment timpoint: mdesc use1 if (condition1 condition2) > >by treatment timpoint: mdesc use2 if (condition3 condition4) > >and so on. > > >Now I want to combine all these counts for all timepoints and treatment >groups to get a single table that I can export to Excel. Is there any >way I >could do that? * * 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/

**References**:**st: combining frequency tables***From:*Shehzad Ali <sia500@york.ac.uk>

**st: RE: combining frequency tables***From:*"Nick Cox" <n.j.cox@durham.ac.uk>

**Re: st: RE: combining frequency tables***From:*Shehzad Ali <sia500@york.ac.uk>

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