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

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: RE: suggestion for missing() |

Date |
Tue, 16 Sep 2008 08:15:41 -0400 |

Apologies to anyone who was confused or misled by my terminology. I would still like to see a function -missing()- which takes a varlist. cheers, Jeph Nick Cox wrote:

In case it gets lost, I'll stick in here a reminder that -dropmiss-

exists to do what Jeph does in his examples. -search- for locations.

On the main point:

I've wanted something like this more than once, so I sympathise.

Whether this is really a good idea I don't know. It may look cosmetic,

but it is rather a fundamental change to Stata's syntax, and it would

introduce a diversity of allowable syntaxes when consistency is arguably

a very good thing.

If this were done, then it should be done consistently across similar

functions such as -max()- and -min()- as well.

Jeph, however, I think introduces some red herrings here. Choice of

terminology confuses the several intersecting issues. Some of the fault

is Stata's in that when -egen- was introduced the members of its family

were called -egen- functions. I don't have a better name to suggest, but

I think this similarity has been widely (although not deeply) confusing.

First off, note that despite similar names functions and -egen-

functions are really quite different beasts. Stata's functions are not

that different from functions in many other languages, but -egen-

functions are very idiosyncratic. The name really is exact: -egen-

functions work __only__ with -egen-.

Jeph mentions -rowmiss()- and -rowtotal()- and calls them row operators.

They are, strictly, -egen- functions. The fact that they are defined to

work across rows, meaning strictly observations, is just that, a fact.

-egen- functions could have any syntax for their argument that you

wanted. Some syntaxes would seem perverse but anything programmable is

possible so long as it passes -egen-.

Jeph then goes on to talk about column operators, but here his informal

use of terminology becomes, potentially, rather misleading.

Operators in most languages, although certainly not all, seem to be

distinguished from functions largely by whether they are implemented via

special symbols (e.g. + - * | &) or via names. That is an accident of

implementation which we could ponder, but, keeping to the point, let me

just underline that when Jeph says column operators I think he means

Stata functions, strict sense.

Such functions are not designed to work with columns, meaning strictly

variables, or indeed anything in particular. They are designed to work

with anything that satisfies their syntax. Whether I say

-missing(1,2,3,4)- or -missing(a[1], a[2], a[3], a[4])- or -missing(x,

y, z)- is all one to -missing()- so long as the arguments fit the

syntax. The results in context will differ because the rest of Stata is so

smart, but I think -missing()- is just a mindless machine.

This is mostly just yet another plea to use Stata's terminology when

discussing Stata!

Nick

n.j.cox@durham.ac.uk

Jeph Herrin

This is mostly a suggestion to StataCorp, perhaps it

has been made or explained elsewhere.

The function -missing()- is quite useful, but I'd

like to propose that it be modified to take a -varlist-

as argument.

First, it would be even more useful if one could specify

many variable names using short hand. Eg, why not

drop if missing(q1-q23)

or

drop if missing(_all)

?

Second, this would be consistent with other row operators

such as -rowmiss- & -rowtotal-, which take varlists. At

least, it seems like that is the Stata convention - row

operators take varlists, column operators take comma

separated lists. Perhaps I'm wrong on this, but it seems

enough of a convention that I invariable try to stick a

varlist in -missing()- anyway.

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**References**:**st: suggestion for missing()***From:*Jeph Herrin <junk@spandrel.net>

**st: RE: suggestion for missing()***From:*"Nick Cox" <n.j.cox@durham.ac.uk>

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