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From |
Nick Cox <njcoxstata@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Extract year of maximum production |

Date |
Sat, 20 Oct 2012 09:18:35 +0100 |

There is a review of working row-wise in SJ-9-1 pr0046 . . . . . . . . . . . . . . . . . . . Speaking Stata: Rowwise (help rowsort, rowranks if installed) . . . . . . . . . . . N. J. Cox Q1/09 SJ 9(1):137--157 shows how to exploit functions, egen functions, and Mata for working rowwise; rowsort and rowranks are introduced which is accessible to all under the SJ's 3-year rule. -search rowwise- to get a clickable link. You have already alluded to two key principles in this territory 1. A -reshape long- can make a row-wise problem easier. 2. There are -egen- functions for row problems. Even more important than #2 is 3. You can solve many problems with a loop over variables. as #2 is just an application of #3. With 3000-odd counties there may well be ties, i.e. counties for which two or more years show the same maximum. Let's be alert to that amd use a slightly odd technique. (Others will be suggested by my paper referred to above.) Starting with your idea egen maxprod = rowmax(timber????) let's initialise a string variable gen whenmax = "" Now whenever we find a year when the maximum occurred we add that year to our string * isn't that 101 years? no matter qui forval y = 1910/2010 { replace whenmax = whenmax + "`y' " if timber`y' == maxprod } Note the extra space in the " " above. In most counties there will be a single year when there was a maximum gen when = real(whenmax) if wordcount(whenmax) == 1 And you can look at the cases with ties to think what you want to do with them: l county whenmax if wordcount(whenmax) > 1 Notes. To extract words from a string, use -word()-. If you have counties with 0 values, they might as well be -mvdecode-d to missing before you calculate your maximum. Extreme case: a county with 0s in every year; iit is absurd to say that the maximum production occurred in every year. (Or you might just -drop- such counties.) Similarly, this technique assumes that there aren't so many ties that the years can't be fit in a -str244- variable and if that's wrong you may need a different technique Nick On Sat, Oct 20, 2012 at 4:10 AM, Daniel Escher <descher@nd.edu> wrote: > I have 100 years of timber production data for all counties in the US > (~3,100). The data are currently in wide format - i.e., timber1910, > timber1911 ... timber2010 (but I can switch them to long if needed). > > I would like to extract the year of maximum timber production for each > county and put that year in a variable called "peakyr." Two things I > thought might be helpful: 1) I can use -egen newvar = rowmax...- to get the > maximum value of a row. 2) I can separate the stub and the year in the > variable name using the -substr- function. Unfortunately, I don't know how > to make those two processes "talk" to each other - if they are even the > right ones to use. > > Stata/IC 12.1 for Windows (32-bit) > Revision 01 Oct 2012 * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: st: Extract year of maximum production***From:*Daniel Escher <descher@nd.edu>

**References**:**st: Extract year of maximum production***From:*Daniel Escher <descher@nd.edu>

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