Thread: concatenate

Hi guys. I wanted to build a function with a variable number of arguments that is able to concatenate in the same vector the vectors given as input (that can be 2,3, 100). I was thinking to something like this

Code:

void concatenate(double *res, double *vec1, int length_vec1, ...)
{

}

I tried to use va_args/start ecc but they seem (up to me) to handle only scalars...Has anyone a hint?

You've to make sure that res has enough space.
scalars ? Are you perl programmer?! :P

Code:

     
             va_list ap;
             va_start(ap,length_vec1); 
             arg = va_arg(ap,double*);

Originally Posted by Bayint Naung

You've to make sure that res has enough space.
scalars ? Are you perl programmer?! :P

Code:

     
             va_list ap;
             va_start(ap,length_vec1); 
             arg = va_arg(ap,double*);

OOOOOOOOK! For res there are no problems...No, I am only a poor statistician that is reaching for speed :-) . Now I am going to use your hint!
Thanks a lot!

I wonder if is it possible to handle vectors with variable length, I mean

Code:

void concatenate(double *res, double *vec1, int length_vec1, double *vec2, int length_vec2)
{
...
}

?

What are you trying to do?

I am trying to do a function that is able to concatenate a variable number of vectors, e.i.

Code:

concatenate(res,vec1,length_vec1,vec2 ,length_vec2) or
concatenate(res,vec1,length_vec1,vec2 ,length_vec2, vec3 ,length_vec3)

and so on. Maybe is more feasible to group the length of the vectors

Code:

concatenate(res,length_vec1,length_vec2,vec,vec21)

E.g variable argument function.

Code:

void show_strs(char *s,...)
{
    va_list ap;
    va_start(ap,s);
    do {
      printf ("%s\n",s);
      s = va_arg(ap,char * );
   } while( s != NULL );
   va_end(ap);

}
call it like this:

  show_strs("hello", "world","variable",(char*) 0 );
  show_strs("only one string",(char*) 0 );
  show_strs("This is a ","1st","2nd","3rd","4th","end",(char*) 0);

Originally Posted by Bayint Naung

E.g variable argument function.

Code:

void show_strs(char *s,...)
{
    va_list ap;
    va_start(ap,s);
    do {
      printf ("%s\n",s);
      s = va_arg(ap,char * );
   } while( s != NULL );
   va_end(ap);

}
call it like this:

  show_strs("hello", "world","variable",(char*) 0 );
  show_strs("only one string",(char*) 0 );
  show_strs("This is a ","1st","2nd","3rd","4th","end",(char*) 0);

of course, but with the difference that I use only arrays of numbers. This is, up to me, the main difficulty I have found in doing this function.

Post your code snippet and a sample of the data you're trying to manipulate.

Originally Posted by itCbitC

Post your code snippet and a sample of the data you're trying to manipulate.

ok...I post you my barbarian solution ;-) to the problem. Here it is the case where I have to concatenate 3 vectors

Code:

void cb_c3(double *res, int *n1, int *n2, int *n3, double *vec1, double *vec2, double *vec3)
{
	int i;
	for( i=0 ; i<*n1 ; i++) res[i] = vec1[i];
	for( i=0 ; i<*n2 ; i++) res[i+*n1] = vec2[i];
	for( i=0 ; i<*n3 ; i++) res[i+*n1+*n2] = vec3[i];
}

Now, my standard glod will be a function tha looks like this

Code:

void cb_c3(double *res,  int n1, double *vec1, ...)
{
...
}

where I put the different lengths of the vectors and the first pointer to the vector.
Do you understand? Does anyone knows R? There is a function called c() that concatenates vectors or scalars in the order they appear. This is what I want

Originally Posted by Elysia

You want to put together different types of vectors, as they are called in mathematics, to a single one (note the emphasis on types)? Or just the same type, and if so, what type?

I want to pool only vectors of doubles or integers

Originally Posted by grumpy

Yeah, I know R and understand.

With variable argument lists, C does not have any means to implicitly detect the number of arguments passed. You'll need to either pass the number of vectors explicitly or look for a marker indicating the last vector.

A function of the form;

Code:

void c(double *result, int number_of_vectors, ...)

will do the trick. After the number_of_vectors argument, interpret the arguments in pairs (eg an int specifying number of elements in the vector, a pointer to the first element).

What it is not clear is how to tell C with va_ that I am handling vectors and not scalars. All the examples I have seen deals with scalars or with strings.