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From |
Richard Williams <Richard.A.Williams.5@nd.edu> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: RE: Taking averages, etc. |

Date |
Wed, 17 Dec 2003 07:15:37 -0500 |

At 10:55 AM 12/17/2003 +0000, Nick Cox wrote:

That is very interesting Nick and something I might well have screwed up sooner or later. Form 1 looks very much like the SPSS if command; but it works very differently. Form 2 is what SPSS users will want as their equivalent to the SPSS if.Non-programmers should note the crucial difference in principle between 1. if <condition> <command> and 2. <command> if <condition> Form 1 carries out _one_ test of the <condition> supplied. If it is true, <command> is carried out, but not otherwise. Form 2 carries a test of the <condition> supplied for _every_ observation specified and then carries out <command> for the observations for which it is true.

I'm probably just missing it, but it seems that Stata does not have a convenient if-then-else structure, i.e. the equivalent of SPSS's DO IF command. In SPSS, I could do something like

DO IF X1 = 1 and X2 = 3

Compute Y = 3.

ELSE IF X3 = 2 and X4 = 17

Compute Y = 4.

ELSE

Compute Y = 5.

END IF.

In SPSS, this would result in Y equaling 3, 4, 5, or missing for all cases. If, say, X1 = 1, X2 = 3, X3 = 2, X4 = 17, Y would be coded 3, i.e. only the first compute would be executed.

In stata, it seems to me like I would have to write increasingly complicated if statements to achieve the same thing; something like

gen y = 3 if X1==1 & X2==3

replace y = 4 if X1 !=1 & X2 !=3 & X3==2 & X4==17

replace y = 5 if X1 !=1 & X2 !=3 & X3 !=2 & X4 !=17

or something like that. Is that correct, or is there an easier way I am overlooking?

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Richard Williams, Associate Professor

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**Follow-Ups**:**Re: st: RE: Taking averages, etc.***From:*Allan Reese <R.A.Reese@hull.ac.uk>

**Re: st: RE: Taking averages, etc.***From:*Fred Wolfe <fwolfe@arthritis-research.org>

**References**:**st: Taking averages, etc.***From:*"de la Garza, Adrian" <ADelagarza@imf.org>

**st: RE: Taking averages, etc.***From:*"Nick Cox" <n.j.cox@durham.ac.uk>

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