How to use call dynamic_array right?

Question

I have try to write a user-defined function MinDis() and apply it in data step, this function is used to compute the minimum distance from one point to each element of an (numeric)array. Code fllowing:

proc fcmp outlib = work.funcs.Math;
    function MinDis(Exp,Arr[*]);
        array dis[2] /symbols;
        call dynamic_array(dis,dim(Arr));
        do i = 1 to dim(Arr);
            dis[i] = abs((Exp - Arr[i]));
        end;
        return(min(of dis[*]));
    endsub;
quit;

option cmplib=work.funcs ; 

data MinDis;
    input LamdazLower LamdazUpper @;
    cards;
    2.50 10.0
    2.51 10.8
    2.49 9.97
    2.75 9.50
    ;
run;

data _null_;
    set ;

    array _PTN_ [14] _temporary_ (0.5,1,1.5,2,2.5,3,4,5,6,7,8,9,10,12);
    StdLamZLow = MinDis(LamdazLower,_PTN_);
    StdLamZUpp = MinDis(LamdazUpper,_PTN_);
    put _all_;
run;

It was compile rightly but gave wrong results. StdLamZLow just get the minimum distance from LamdazLower to the first two element of array _PTN_.

When I rewrite the dim of dis as 999 or something very big and get rid of call dynamic_array statement I would get it right. But I surely want to know why min(of dis[*]) just take dis as a 2-dim array.

By the way, how can I use implied DO-loops do over ... to instead of explicit DO loops? I have tried several times but haven`t success yet.

Thanks for any hints.

Answer 1

I think this happens cause of dynamic array. MIN function see just static length of dis array(2 in your case). So you should try to compute min of array without calling MIN function:

proc fcmp outlib = work.funcs.Math;
    function MinDis(Exp,Arr[*]);
        length=dim(Arr);
        array dis[2] /nosymbols;
        call dynamic_array(dis,length);
        dis[1]=abs((Exp - Arr[1]));
        min=dis[1];
        do i = 1 to length;
            dis[i] = abs((Exp - Arr[i]));
            if dis[i] < min then min=dis[i];
        end;
        return(min);
    endsub;
quit;

Output:

LamdazLower=2.5 LamdazUpper=10 StdLamZLow=0 StdLamZUpp=0

LamdazLower=2.51 LamdazUpper=10.8 StdLamZLow=0.01 StdLamZUpp=0.8

LamdazLower=2.49 LamdazUpper=9.97 StdLamZLow=0.01 StdLamZUpp=0.03

LamdazLower=2.75 LamdazUpper=9.5 StdLamZLow=0.25 StdLamZUpp=0.5

In addition about implied DO-loops(here on 6th page), if i correctly understood the question:

data temp;
array dis dis1-dis4;
do over dis;
   dis=2;
   put _all_;
end;
run;

Output:

I=1 dis1=2 dis2=. dis3=. dis4=. ERROR=0 N=1

I=2 dis1=2 dis2=2 dis3=. dis4=. ERROR=0 N=1

I=3 dis1=2 dis2=2 dis3=2 dis4=. ERROR=0 N=1

I=4 dis1=2 dis2=2 dis3=2 dis4=2 ERROR=0 N=1