Add function to filter data structure

Only works on flat structures right now.  This should be used and
let-bound to a variable when that variable is going to be used a lot.
Theoretically, it should be faster than traversing through the entire
data structure.  Think of this as a Emacs-local version of the API's own
filter.

2 files changed, 23 insertions, 0 deletions

diff --git a/stack-core.el b/stack-core.el
index d48c873..cf7dde5 100644
--- a/stack-core.el
+++ b/stack-core.el
@@ -209,5 +209,14 @@ entire response as a complex alist."
 			     stack-core-remaining-api-requests))
 	    (cdr (assoc 'items response))))))))
 
+(defun stack-core-filter-data (data desired-tree)
+  "Filters DATA and returns the DESIRED-TREE"
+  (delq
+   nil
+   (mapcar (lambda (cons-cell)
+	     (when (member (car cons-cell) desired-tree)
+	       cons-cell))
+	   data)))
+
 (provide 'stack-core)
 ;;; stack-core.el ends here
diff --git a/tests.el b/tests.el
index c79cfc4..0c520d8 100644
--- a/tests.el
+++ b/tests.el
@@ -25,3 +25,17 @@
   "Test a method given a bad set of keywords"
   (should-error
    (stack-core-make-request "questions" '(()))))
+
+(ert-deftest test-data-filter-1 ()
+  "Test the meta-convenience function"
+  (should
+   (equal
+    '((1 . t) (2 . [1 2]) (3))
+    (stack-core-filter-data '((0 . 3)
+			      (1 . t)
+			      (a . five)
+			      (2 . [1 2])
+			      ("5" . bop)
+			      (3)
+			      (p . 4))
+			    '(1 2 3)))))