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From |
Jeph Herrin <junk@spandrel.net> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: RE: programming problem |

Date |
Fri, 17 Aug 2007 09:34:58 -0400 |

Never noticed -concat- before. Nice. thanks, Jeph Nick Cox wrote:

This problem is, in my view, an awkward little challenge.

I very nearly posted a solution that was _quite_ wrong.

A -reshape- solution, as exemplified by Sebastian's code,

looks awkward for just this problem, but may of course be a good

idea for a variety of other problems.

A quite different idea runs like this:

egen history = concat(var1-var12) gen byte mycond = substr(history, month, 1) == "1"

The appearance here of avoiding a loop over variables

is illusory, as a loop is hidden inside -concat()- (and even as of Stata 10 it is still a -while- loop).

But a concatenated history makes some other problems easy, even with this wide data structure.

Has this person experienced a spell of three or more months with this condition?

gen byte spell3 = strpos(history, "111") > 0

When was the first month in the year with this condition?

gen byte first = strpos(history, "1")

When was the last month in the year with this condition?

gen byte first = cond(first, 13 - strpos(reverse(history), "1"), 0)

Nick n.j.cox@durham.ac.uk

Jeph Herrin

Nick CoxDuh. I had done this: forval j = 1/12 { replace mycond = `j' == month & var`j' == 1 } Which effectively only tests month 12, before I veered off in another direction.

Jeph HerrinShort of a solution using -reshape-, I think

this will suit:

gen mycond = 0 forval j = 1/12 { replace mycond = 1 if `j' == month & var`j' == 1 }

where I assume that your -var*- are 1 when true.

I have observations on patient admissions over a 12 month period. For each observation, I have 12 variables, call them var1-var12, which indicate whether a certain condition was met for that patient for months 1-12. So, eg, it may be true for months 1-3 and 7-12. I also have a variable -month-, which indicates the current month of the observed admission. What I want to capture is whether the condition was true in the month of admission. For instance, at first I unthinkingly tried this: gen mycond = var`=month'==1 but this of course uses the first observed value of -month-, which happens to be 6, and only checks -var6-. I eventually got there by creating lots of vars, but is there a more direct solution?* * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

* * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**RE: st: RE: programming problem***From:*"Nick Cox" <n.j.cox@durham.ac.uk>

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