Data update

Task/Associative-array-Merging/Common-Lisp/associative-array-merging-3.lisp

@@ -0,0 +1,28 @@
+(defun merge-hash-tables (hashtable &rest other-hashtables)
+  (let ((result (make-hash-table :test (hash-table-test hashtable))))
+    (dolist (ht (list* hashtable other-hashtables))
+      (maphash #'(lambda (k v) (setf (gethash k result) v)) ht))
+    result))
+
+;; aux functions
+(defun make-hash-table-from-alist (alist &key (test 'equal))
+  (let ((result (make-hash-table :test test)))
+    (loop for (k . v) in alist
+          do (setf (gethash k result) v))
+    result))
+(defun make-alist-from-hash-table (hashtable)
+  (let ((result ()))
+    (maphash #'(lambda (k v) (setf result (acons k v result))) hashtable)
+    (nreverse result)))
+
+;; solving the task
+(let ((base (make-hash-table-from-alist '(("name" . "Rocket Skates")
+                                          ("price" . 12.75)
+                                          ("color" . "yellow"))))
+      (update (make-hash-table-from-alist '(("price" . 15.25)
+                                            ("color" . "red")
+                                            ("year" . 1974)))))
+  (format t "base: ~a~%update: ~a~%merged: ~a~%"
+          (make-alist-from-hash-table base)
+          (make-alist-from-hash-table update)
+          (make-alist-from-hash-table (merge-hash-tables base update))))