Re: st: Re: Converting a SAS datastep to Stata

[Daniel Feenberg <feenberg@nber.org>]

On Mon, 13 Dec 2010, Kevin Geraghty wrote:

> FYI, I tried this to satisfy my own curiosity; it works. Probably the most parsimonious approach.
> assuming your dataset has a variable "year" defined, taking values from 1993 through 2008, and the values specified for "exmp" are in the correct ascending year order.
>
> matrix input exmp=(2350, 2450, 2500, 2550, 2650, 2700, 2750, 2800, 2900, 3000, 3050, 3100, 3200, 3300, 3400, 3500)
> gen int exemption = exmp[1,year-1992]

Thank you! I just repeated your test. This will be much more efficient 
than the ways I had thought of or have been suggested so far.  I am very 
pleased that it doesn't require a wholesale conversion to Mata - I get to 
keep the implicit index over returns and I can generate the code above 
directly from the existing SAS code.

Sorry I got the number of elements to the vector wrong in my SAS example 
- the number of initializers should equal the number of array elements or 
I will get the wrong answer.

BTW, anyone looking for the existing stata callable fortran version should

   net from "http://www.nber.org";
   net describe taxsim9

That version covers federal tax from 1960-2013 and state income taxes 
from 1979-2009.

Thanks again,

Daniel Feenberg



> ----- "Joseph Coveney" <jcoveney@bigplanet.com> wrote:
>
> > Daniel Feenberg wrote:
> >
> > I have done programs to calculate income tax liability in SAS and
> > fortran.
> > Both those languages allow tax parameters that vary across years and
> > filing status to be held in initialized arrays. For example, in SAS
> > one
> > could declare:
> >
> >     array exmp(1993:2010) _temporary_;
> >     retain exmp 2350 2450 2500 2550 2650 2700 2750 2800 2900 3000 3050
> > 3100
> >                 3200 3300 3400 3500;
> >
> > and then assigning the correct value of the personal exemption to
> > every
> > individual record is just:
> >
> >     exemption = exmp(fldpyr);
> >
> > where flpdyr is a variable in the data with the filing year. I am at a
> > bit
> > of a loss as to how to do this in Stata. I don't like:
> >
> >     gen exemption = (flpdyr==1993)*2350 + (flpdyr==1994)*2450...(for
> > 18
> > subexpressions in all)
> >
> > or
> >
> >     gen     exemption = 2350, if flpdyr==1993
> >     replace exemption = 2450, if flpdyr==1994
> >     ...(for 18 lines in all)...
> >
> > because these require (and execute) so much repetitive code.
> >
> > Another possibility is to create a dataset of parameters by year and
> > filing status, then sort the tax return data by year and filing
> > status,
> > and finally merge the parameters onto the tax return data. But that
> > requires a sort and a lot of I/O, which could be slow with potentially
> >
> > millions of returns. The additional memory required is probably not a
> > big
> > issue.
> >
> > I don't actually know Mata, but I think I could define a rowvector:
> >
> >      exmp =  ( 2350 2450 2500 2550 2650 2700 2750 2800 2900 3000 3050
> > 3100
> >                 3200 3300 3400 3500);
> >
> > and then loop over all the tax returns executing:
> >
> >      exemption[i] = exmp[flpdyr[i]-1992];
> >
> > for each return (where i indexes returns). That seems to mean that
> > every
> > variable is going to have to carry around a [i] subscript and there
> > will
> > be a 1,000 lines of Mata code executed for each return (rather than
> > the
> > preferred 1,000 lines of code for all the returns together). That is
> > much
> > less attractive than leaving the observation number implicit, as the
> > regular Stata language does. Brief study of [M-2]subscripts doesn't
> > suggest any "matrixy" way of coding this.
> >
> > I expect I am missing something obvious, can someone point me in the
> > right
> > direction?
> >
> > --------------------------------------------------------------------------------
> >
> > The number of years is limited and they're integers, so you could
> > probably get
> > away with value labels and a one-shot work-up (see below).  This
> > SAS-ish
> > approach might be faster than any -merge- (with its implicit -sort-)
> > when you
> > have millions of observations in the tax-record dataset.
> >
> > I'd bet that becoming familiar with Mata's -asarray()- (think: Paul
> > Dorfman)
> > will be more gratifying in the long run.
> >
> > Joseph Coveney
> >
> > P.S.  What does SAS do when you have more index values (18 years) than
> > array
> > values (16 exemptions)?  Does it pad the last value out to the end of
> > the array,
> > or recycle à la R?
> >
> > version 11.1
> >
> > clear *
> > set more off
> > set obs 18
> > generate int year = 1992 + _n
> >
> > *
> > * Begin here
> > *
> > local value_label label define Exemptions
> > local year 1993
> > foreach exemption in 2350 2450 2500 2550 2650 ///
> >     2700 2750 2800 2900 3000 3050 3100 3200 ///
> >     3300 3400 3500 3550 3600 {
> >     local value_label `value_label' `year' "`exemption'"
> > 	local ++year
> > }
> > `value_label'
> > label values year Exemptions
> > decode year, generate(exemption)
> > _strip_labels year
> > destring exemption, replace
> > list, noobs abbreviate(20) separator(0)
> > exit
> >
> >
> >
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>
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