Combine raisins and apple juice in a microwave-safe bowl; microwave at HIGH for 30 seconds. Let stand 2 minutes; drain. Combine raisins, celery, apple, and walnuts in a medium bowl. Stir in mayonnaise and yogurt.
"I developed this recipe to cut down on the fat content of the original Waldorf salad, which was dressed with heavy mayonnaise." --M. Georgene Laffey, Pinehurst, NC