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Re: st: Mata: Recursive structures and pointers
Ulrich Kohler <[email protected]> inquired about implementing
a linked list in Mata. This is what I came up with.
mata
struct listelem {
real scalar a
real scalar b
pointer(struct listelem scalar) scalar nextpoint
}
struct listelem scalar function setelem(real scalar s)
{
struct listelem scalar e
e.a=s
e.b=s
return(e)
}
struct pointlist {
struct listelem scalar first
pointer(struct listelem scalar) scalar last
}
struct pointlist scalar function setpoint( real vector seq)
{
struct pointlist scalar v
real scalar i
real scalar l
l = length(seq)
if (l == 0) return(v)
v.first.a = seq[1]
v.first.b = seq[1]
v.last = &(v.first)
liststruct(v)
for (i=2; i<=l; i++) {
v.last->nextpoint = &setelem(seq[i])
v.last = v.last->nextpoint
}
return(v)
}
void function testit()
{
real scalar i
real colvector v
pointer(struct listelem scalar) scalar el
struct pointlist scalar l
v = 1::10
l = setpoint(v)
liststruct(l)
printf("first\n")
el = &(l.first)
liststruct(*el)
i = 1
while(el->nextpoint!=NULL) {
printf("\nnext %g\n", ++i)
printf("el = ")
el
printf("next = ")
el->nextpoint
printf("\n")
el = el->nextpoint
liststruct(*el)
}
}
end
. mata: testit()
1 structure of 2 elements
1.1 structure of 3 elements
1.1.1 1 x 1 real = 1
1.1.2 1 x 1 real = 1
1.1.3 1 x 1 pointer = NULL
1.2 1 x 1 pointer != NULL
1 structure of 2 elements
1.1 structure of 3 elements
1.1.1 1 x 1 real = 1
1.1.2 1 x 1 real = 1
1.1.3 1 x 1 pointer != NULL
1.2 1 x 1 pointer != NULL
first
1 structure of 3 elements
1.1 1 x 1 real = 1
1.2 1 x 1 real = 1
1.3 1 x 1 pointer != NULL
next 2
el = 0x9022868
next = 0x9020b68
1 structure of 3 elements
1.1 1 x 1 real = 2
1.2 1 x 1 real = 2
1.3 1 x 1 pointer != NULL
next 3
el = 0x9020b68
next = 0x9022738
1 structure of 3 elements
1.1 1 x 1 real = 3
1.2 1 x 1 real = 3
1.3 1 x 1 pointer != NULL
next 4
el = 0x9022738
next = 0x90208b8
1 structure of 3 elements
1.1 1 x 1 real = 4
1.2 1 x 1 real = 4
1.3 1 x 1 pointer != NULL
next 5
el = 0x90208b8
next = 0x9026758
1 structure of 3 elements
1.1 1 x 1 real = 5
1.2 1 x 1 real = 5
1.3 1 x 1 pointer != NULL
next 6
el = 0x9026758
next = 0x9020e98
1 structure of 3 elements
1.1 1 x 1 real = 6
1.2 1 x 1 real = 6
1.3 1 x 1 pointer != NULL
next 7
el = 0x9020e98
next = 0x90225e8
1 structure of 3 elements
1.1 1 x 1 real = 7
1.2 1 x 1 real = 7
1.3 1 x 1 pointer != NULL
next 8
el = 0x90225e8
next = 0x9026578
1 structure of 3 elements
1.1 1 x 1 real = 8
1.2 1 x 1 real = 8
1.3 1 x 1 pointer != NULL
next 9
el = 0x9026578
next = 0x90269d8
1 structure of 3 elements
1.1 1 x 1 real = 9
1.2 1 x 1 real = 9
1.3 1 x 1 pointer != NULL
next 10
el = 0x90269d8
next = 0x90214b8
1 structure of 3 elements
1.1 1 x 1 real = 10
1.2 1 x 1 real = 10
1.3 1 x 1 pointer = NULL
-Rich
[email protected]
>
> ------------------------------------------------xyz.mata---
> ...
> struct listelem {
> real scalar a
> real scalar b
> pointer(struct listelem scalar) scalar nextpoint
> }
>
> struct listelem scalar function setelem(real scalar s) {
> struct listelem scalar e
> e.a=s
> e.b=s
> return e;
> }
>
> ------------------------------------------java code-----------
> public class listelem {
>
> public int a;
> public int b;
> public listelem nextpoint;
>
> public void setelem(int s){
> a=s;
> b=s;
> }
> }
>
>
> public class pointlist {
>
> public listelem first; //the first element of the list
> public listelem last; //the last element of the list
>
>
> //initialisation of the first element
> pointlist(int k){
> first = new listelem();
> first.a = k;
> first.b = k;
> last = first;
> }
>
>
> public static pointlist setpoint(int[] seq){
>
> pointlist v; //return linked list
> int length; //length of the argument vector seq
>
> v = new pointlist(seq[0]);
> length = seq.length;
>
> //filling out of the list
> for(int i=1; i<length; i++){
> listelem newelem = new listelem();
> newelem.setelem(seq[i]);
>
> v.last.nextpoint = newelem;
> v.last = v.last.nextpoint;
> }
> return v;
> }
> -----------------------------------------------------------
>
> Now let us turn to our attempts to implement this in Mata.
> Basically we have defined the structure "pointlist" that implements a "linked
> list" of points (a,b) and a function "setpoint" that fills out this list with
> the values of the argument vector "seq". Below is how far we got. We have
> indicated the line that causes trouble with a comment.
>
> ------------------------------------------------xyz.mata---
> ...
> struct pointlist {
> struct listelem scalar first
> pointer(struct listelem scalar) scalar last
> }
>
>
> struct pointlist scalar function setpoint( real vector seq) {
>
> struct pointlist scalar v
> real scalar i
> real scalar length
>
> length = length(seq)
> v.first.a = seq[1]
> v.first.b = seq[1]
> v.last = &v.first
> liststruct(v)
>
>
> for (i=2; i<=length; i++) {
>
> struct listelem m
> m= setelem(seq[i])
> v.last.nextpoint= m // <- See error message below
> v.last = &last.nextpoint
> }
> return(v)
> }
> ...
> -----------------------------------------------------------
>
> Compiling this code we receive the following error message at the indicated
> line:
>
> ------------------------------------------------------------
> type mismatch: exp.exp: pointer found where struct expected
> -------------------------------------------------------------
>
> We somehow stick with this error message. Our main problem, however, concerns
> the using of pointers. The pointer "last" should move along the list and
> always point to the last element of the list (it means, it should allow to
> set a new point at the end of the list). It does not work. How can we add a
> new element at the end of the list?
>
> Many regards
>
> Uli and Magdalena
>
> --
> [email protected], [email protected]
> +49 (030) 25491-361
> *
> * For searches and help try:
> * http://www.stata.com/support/faqs/res/findit.html
> * http://www.stata.com/support/statalist/faq
> * http://www.ats.ucla.edu/stat/stata/
*
* For searches and help try:
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* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/
