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# Re: st: -svmat- with matrix colnames based on factor variable names?

 From To Subject Re: st: -svmat- with matrix colnames based on factor variable names? Date Sat, 12 Feb 2011 10:49:48 -0000

```Thanks to Nick Cox, Austin Nichols and Scott Merryman for their
responses. Scott's message pointed, inter alia, to a useful Statalist
posting by himself, and also to a Stata News article in which graphing
after -margins- is usefully accomplished using Roger Newson's -parmest-
(on SSC). The small, but perhaps important, difference in my case is
that the x-axis variable in my proposed graphs are categorical (factor
variable values) rather than continuous (age in years in the News and
Scott's examples).  As Nick and Austin suggest, some pre- or
post-processing of the colnames/factor varlist is inevitable. Austin
kindly offered some assistance were I to suggest an example based on
public data. Here's one inspired by Scott's earlier example [I've added
use of variable hsizgp, which is categorical taking values 1(1)5]:

. webuse nhanes2f, clear

. logit diabetes i.hsizgp  i.black i.female age i.female#c.age, nolog

Logistic regression                               Number of obs   =
10335
LR chi2(8)      =
391.83
Prob > chi2     =
0.0000
Log likelihood = -1803.1523                       Pseudo R2       =
0.0980

------------------------------------------------------------------------
------
diabetes |      Coef.   Std. Err.      z    P>|z|     [95% Conf.
Interval]
-------------+----------------------------------------------------------
------
hsizgp |
2  |  -.1797069   .1280784    -1.40   0.161    -.4307359
.0713221
3  |     .11717   .1621709     0.72   0.470    -.2006792
.4350192
4  |   .3391857   .1847375     1.84   0.066    -.0228931
.7012645
5  |  -.0473484   .1967049    -0.24   0.810    -.4328829
.3381862
|
1.black |   .6699473   .1286628     5.21   0.000     .4177728
.9221217
1.female |   1.435121    .489943     2.93   0.003     .4748507
2.395392
age |   .0766945   .0066901    11.46   0.000      .063582
.0898069
|
female#c.age |
1  |  -.0213554   .0079371    -2.69   0.007    -.0369117
-.005799
|
_cons |  -7.403102   .4346565   -17.03   0.000    -8.255013
-6.551191
------------------------------------------------------------------------
------

. margins , at(female = 1  age = 40 hsizgp = (1(1)5) ) post

Predictive margins                                Number of obs   =
10335
Model VCE    : OIM

Expression   : Pr(diabetes), predict()

1._at        : hsizgp          =           1
female          =           1
age             =          40

2._at        : hsizgp          =           2
female          =           1
age             =          40

3._at        : hsizgp          =           3
female          =           1
age             =          40

4._at        : hsizgp          =           4
female          =           1
age             =          40

5._at        : hsizgp          =           5
female          =           1
age             =          40

------------------------------------------------------------------------
------
|            Delta-method
|     Margin   Std. Err.      z    P>|z|     [95% Conf.
Interval]
-------------+----------------------------------------------------------
------
_at |
1  |   .0250719   .0038488     6.51   0.000     .0175283
.0326154
2  |   .0210404    .002844     7.40   0.000     .0154662
.0266145
3  |   .0280953   .0041529     6.77   0.000     .0199558
.0362348
4  |   .0348208   .0053377     6.52   0.000     .0243591
.0452825
5  |    .023942   .0040474     5.92   0.000     .0160092
.0318748
------------------------------------------------------------------------
------

. matrix at = e(at)

. mat li at

at[5,10]
1b.      2.      3.      4.      5.     0b.      1.     0b.
1.
hsizgp  hsizgp  hsizgp  hsizgp  hsizgp   black   black  female
female     age
r1       1       0       0       0       0       .       .       0
1      40
r2       0       1       0       0       0       .       .       0
1      40
r3       0       0       1       0       0       .       .       0
1      40
r4       0       0       0       1       0       .       .       0
1      40
r5       0       0       0       0       1       .       .       0
1      40

. matnames at // -matnames- from SSC (by Austin Nichols)

. di r(c)
`":1b.hsizgp"' `":2.hsizgp"' `":3.hsizgp"' `":4.hsizgp"' `":5.hsizgp"'
`":0b.black"' `":1.black"' `":0b.female"' `":1.female"' `":age"'

. svmat at

. de at*

storage  display     value
variable name   type   format      label      variable label
------------------------------------------------------------------------
----------------------------------------------------------------
at1             float  %9.0g
at2             float  %9.0g
at3             float  %9.0g
at4             float  %9.0g
at5             float  %9.0g
at6             float  %9.0g
at7             float  %9.0g
at8             float  %9.0g
at9             float  %9.0g
at10            float  %9.0g

. matrix at2 = e(at)

. svmat at2, name(col)
invalid syntax
r(198);

The workaround I was seeking was a quick/easy/automated way of going
from what is shown as the contents of r(c) after -matnames- to a list of
valid variable names that preserves the essential information. The new
list can be used to re-label the matrix prior to -svmat-. The new names
could be based, for instance, on the old ones but drop the ":" and "."
from the elements of r(c), and add some prefix ("_", say) to each of the
elements. My efforts using -subinstr- and also regular expression
functions were not productive, but that is probably a comment on my
skills.

Thanks, Stephen

------------------------------

Date: Fri, 11 Feb 2011 13:02:58 -0600
From: Scott Merryman <scott.merryman@gmail.com>
Subject: Re: st: -svmat- with matrix colnames based on factor variable
names?

On Fri, Feb 11, 2011 at 11:22 AM,  <S.Jenkins@lse.ac.uk> wrote:
> I'm having difficulty using a list of factor variable names to
construct
> the column names of a matrix post-estimation.
>
> This arises when using -margins, over(.)- with multiple -at(.)-
options.
> I want to collect to collect all the estimates in a matrix with one
row
> per at/over combination, with additional columns also containing
values
> for the at values chosen. To keep track, I want the column names for
the
> additional at columns to contain names that identify the factor
> variables.
>
> Overall aim: once I have created the summary matrix , I want to
convert
> each of the columns to a variable, with all the at variables --
together
> with other variables containing estimates and SE -- to be saved to a
> separate mini-dataset, and used for graphing or table processing.

Perhaps the thread  "Graphic displays or results from margins" at:

http://www.stata.com/statalist/archive/2010-09/msg00807.html

or the example in the vol 25 number 3 of The Stata News (
http://www.stata.com/news/statanews.25.3.pdf ) would be useful.

Scott
===============
From: Austin Nichols <austinnichols@gmail.com>
Subject: Re: st: -svmat- with matrix colnames based on factor variable
names?

Stephen--
Why do you need the names option on -svmat-?  You can also write a
little loop to save the matrix to variables/obs on your data, without
putting illegal names on variables. But either way, you will have to
figure out what you want to call a variable that wants to be named
0b.edlevel or whatever.
If you provide an example with public data, I will come up with a few
solutions for you.
===============
------------------------------

Date: Fri, 11 Feb 2011 18:13:36 +0000
From: Nick Cox <n.j.cox@durham.ac.uk>
Subject: st: RE: -svmat- with matrix colnames based on factor variable
names?

I don't have a positive solution but I do note -svmat- was written for
version 4 and so it is indeed unlikely to support factor variables. So
any pre-processing for -svmat- would have to find a work-around for
that.

Nick
n.j.cox@durham.ac.uk
+++++++++++++++

Stephen
-------------------------------------
Professor Stephen P. Jenkins  <s.jenkins@lse.ac.uk>
Department of Social Policy and STICERD
London School of Economics and Political Science
Houghton Street
London WC2A 2AE, U.K.
Tel. +44 (0)20 7955 6527
Survival Analysis using Stata:
http://www.iser.essex.ac.uk/survival-analysis