Re: st: Use of matrix values in generate statements

[Daniel Feenberg <feenberg@nber.org>]

On Sun, 27 Mar 2011, Nick Cox wrote:

> Kit has given the most important answer: Mata is a much richer
> language for handling non-standard problems.

Thanks to all for the suggestions, but the best one came from an offline 
source.

It turns out that you actually can index into an array. This is not 
suggested in the programming manual, but a trial of:

  gen int i=flpdyr-1992
  gen int j=filestat
  gen z=stdvals[i,j]

does seem to work, and is quite fast (3 seconds/million records for the 
last statement).

I think it makes for the clearest code, also. I'd like to keep the code 
straightforward, so that naive users can modify it. (I include myself in 
that category, obviously!)

I have looked again at [U]14.9 and do not see any hint of this valuable 
ability, which perhaps explains why no one mentioned it. In fact, I don't 
believe any plausible interpretation of language given at numbered 
paragraphs 1 and 2 on page 173 of the Release 11 user's guide would allow 
this.

If an index is out of range the value returned is missing, but there is no 
error, which suggests some thought has gone into this feature.

Again thanks for taking an interest,

Daniel Feenberg
NBER
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