# This function sums elements of an array.  If `x' is a scalar, it is
# returned unchanged.  If `x' is a vector, the sum of all of its
# elements is returned.  If `x' is a matrix, a vector is returned
# each element of which is the sum of the elements in the
# corresponding column.

sum = function( x )
{
    return sum.(class(x))(x);
};

sum.scalar = function( x ) { return x; };

( sum.table =
  sum.("function") =
  sum.("NULL") = strip( 
    function( x )
    {
	message( "Invalid argument to sum." );
	exception();
    } )
);

sum.vector = function( v )
{
    local( s );

    if ( v.type == "character" )
    {
	s = "";
	for ( v in v ) { s += v; }

    else

	s = fill( v.ne; 1 ) * v;

    }

    return s;
};

sum.matrix = function( m )
{
    local( c; s );

    if ( m.type == "character" )
    {
	s = fill( m.nc; m );
	for ( c in seq(m.nc) ) { s[c] = sum.vector( m[;c] ); }
	s.eid = m.cid;

    else

	s = fill( m.nr; 1 ) * m;

    }

    return s;
};