RE: st: Evaluate if a dataset is empty

["Seliger Florian" <seliger@kof.ethz.ch>]

Nick:
> The second is that you are planning to create about 10,000 datasets 
> with not much in them. I would instead create a list of names of empty 
> datasets in a local macro, and then with that create a composite 
> dataset with the same stuff, all just once.

Thanks too.
I have already implemented Maarten's suggestion, but could you give exemplary code?

> An overarching question is why you need to pretend that empty datasets 
> are populated, but I guess there is a good reason.

I do not pretend that they are populated, the values are in fact all zero.
In a first stage I calculated counts, but if Stata did not find anything to count it created an empty dataset.

Best,
Florian









-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Maarten Buis
Sent: Donnerstag, 27. März 2014 12:04
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: Evaluate if a dataset is empty

On Thu, Mar 27, 2014 at 11:51 AM, Seliger  Florian wrote:
> I want Stata to go through 20,000 small datasets (with a forvalues loop, datasets are indexed accordingly) and evaluate if the dataset is empty or not. About 50% of the datasets are empty meaning that there are no values for any variable.

capture assert _N == 0
if _rc == 0 {
    set obs 18
    ...
}

The logic is that _N is the number of observations in the dataset, so _N == 0 corresponds to an empty dataset. -assert- gives an error message when the statement is values, but -capture- captures these error messages and leaves the return code behind in _rc. No error message corresponds with an return code 0, so _rc == 0 corresponds with an empty dataset.

Hope this helps,
Maarten

---------------------------------
Maarten L. Buis
WZB
Reichpietschufer 50
10785 Berlin
Germany

http://www.maartenbuis.nl
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