Kit,
I think it works if you define ii (and w) before calling maxindex. Try:
---
m = (
2.9479707, .15\
2.926226 , .16\
2.8994321, .17\
2.8691981, .18\
2.8368784, .19\
2.8035694, .2\
2.7701303, .21\
2.7372142, .22\
2.705299 , .23\
2.6747184, .24)
ii = J(0,0,.)
w = J(0,0,.)
maxindex(m[,1],1,ii,w)
---
Then
:ii
1
: w
1 2
+---------+
1 | 1 1 |
+---------+
And the answer to Le Wang's question would be
m[ii,2]
.15
This example happens to have the max on the first row. Let's move it to the
third
---
j = (2\3\1\4::10)
m2 = m[j,]
maxindex(m2[,1],1,ii,w)
---
: ii
3
: m2[ii,2]
.15
Curiously w is still (1,1). What is it?
Cheers,
Germán
-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Kit Baum
Sent: Sunday, November 05, 2006 2:13 PM
To: statalist@hsphsun2.harvard.edu
Subject: st: return the maximum and corresponding value...
Le Wang said
I have a question regarding Mata. Suppose I have an imaginary matrix
with two columns as follows,
x y
2.9479707 .15
2.926226 .16
2.8994321 .17
2.8691981 .18
2.8368784 .19
2.8035694 .2
2.7701303 .21
2.7372142 .22
2.705299 .23
2.6747184 .24
I want Mata to return the maximum values of column 1 (x) AND its
corresonding values in column 2 (y), in this example, 2.9479707 and
0.15. I understand I can use -rowmax- to find the maximum, but I am
not quite sure how to find the corresponding value.
The good news: there is a function undocumented in the manual to
handle this.
The bad news: it does not appear to work.
This workaround does:
real scalar lewang(real matrix a)
{
real vector i
maxindex(a[.,1],1,i,w)
return(i)
}
a=(4,2\6,3\10,9\1,2\4,5\7,6\9,0)
j=lewang(a)
b=a[j,.]
b
Now all this horsing around should be unnecessary, for you should
just be able to call
maxindex(a[.,1],1,ii,w)
But that yields
<istmt>: 3499 ii not found
r(3499);
minindex() doesn't seem to work either, even on the examples in the
helpfile:
: v = (3,1,5,7,6)
: minindex(v, 1, i, w)
<istmt>: 3499 i not found
r(3499);
Looks like a bug to me.
Kit Baum, Boston College Economics
http://ideas.repec.org/e/pba1.html
An Introduction to Modern Econometrics Using Stata:
http://www.stata-press.com/books/imeus.html
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