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From |
"P. Wilner Jeanty" <pwjeanty@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
st: Re: Saving memory local vs usual variable |

Date |
Sat, 4 Oct 2008 01:14:55 -0400 |

The experts have spoken. Yet, I just want to point to a useful command that was left out of the discussion when it comes to saving in local macros descriptive statistics (stats for short) for more than one variable. I had a problem similar to Ashim's where I wanted the mean for several variables. I dealt with the problem using SUMMARIZE in a loop. But, I kept wondering why is that SUMMARIZE saves results only for the last variable when a varlist is specified? Does not StataCorp think that one might want returned results for all the variables in the varlist? I found the answer to these questions in TABSTAT which offers a lot more flexibility. If one wants to save in local macros several stats for several variables I think TABSTAT with the SAVE option is not to be overlooked. TABSTAT saves results in matrices. Thus, to get the most out of it, some background on macro and matrix manipulation may be a big plus. Let me give some examples using the auto dataset: Suppose I want to save in locals the mean for price, mpg, and weight; I type in: sysuse auto qui tabstat price mpg weight, save // mean is the default The results are saved in a 1x3 matrix called r(StatTotal). I put each mean in a local macro and then display them: ********** mat mym=r(StatTotal) // I don't know why I cannot work with r(StatTotal) itself for some operations loc i=1 foreach v in `: colnames mym' { loc m_`v'=mym[1,`i'] // Here for example, r(StatTotal) fails to behave as a regular matrix. loc ++i } di "mean_price=" `m_price', "mean_mpg="`m_mpg', "mean_wght=" `m_weight' ******** Now suppose I want more than one statistics, say mean and max: qui tabstat price mpg weight, stat(mean max) save Now TABSTAT returns a 2x3 matrix (rows are the stats and columns are variables) that I can use to pick on the mean and/or the max of any variable. First I put each element in a local macro, so I can easily pick on any stats I want. For illustration, I pick a few stats to display. As above, I try to be as general as possible. ****** mat mstat=r(StatTotal) loc i=1 foreach s in `: rownames mstat' { loc j=1 foreach v in `: colnames mstat' { loc `s'_`v'=mstat[`i',`j'] loc ++j } loc ++i } di "mean_price=" `mean_price', "mean_mpg="`mean_mpg', "max_wght=" `max_weight' ***** For verification, I display the contents of the matrix: mat list mstat If I want these stats by car type, I type in: tabstat price mpg weight, by(foreign) stat(mean max) save Now three 2x3 matrices are returned. One for each car type and one for the overall (unconditional) mean and max. I can choose a matrix and pick on any element, row, or column that I want. To display the name of the matrices, type in: ret list For more on tabstat, type in: help tabstat -- P. Wilner Jeanty, Post-Doctoral Researcher Dept. of Agricultural, Environmental, and Development Economics The Ohio State University 2120 Fyffe Road Columbus, Ohio 43210 (614) 292-6382 (Office) * * 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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