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Re: st: Extract year of maximum production


From   Daniel Escher <descher@nd.edu>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Extract year of maximum production
Date   Sat, 20 Oct 2012 10:36:54 -0400

Nick, that worked perfectly. Thank you so much!

egen maxprod = rowmax(timber1910-timber2010)
recode maxprod 0 = .  // I recoded counties without production to
missing for now
gen whenmax = ""
qui forval y = 1910/2010 {
	replace whenmax = whenmax + "`y'  " if timber`y' == maxprod
}
gen when = real(whenmax) if  wordcount(whenmax) == 1

*Yes, 1910-2010 is 101 years.
*I didn't have any duplicates/ties to worry about

On Sat, Oct 20, 2012 at 4:18 AM, Nick Cox <njcoxstata@gmail.com> wrote:
> 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
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