Merge pull request #87 from steventlamb/topic/make_zip_n_ary

Convert -zip to support variable-length arguments

README.md

@@ -133,7 +133,7 @@ Operations dual to reductions, building lists from seed value rather than consum
 * [-interpose](#-interpose-sep-list) `(sep list)`
 * [-interleave](#-interleave-rest-lists) `(&rest lists)`
 * [-zip-with](#-zip-with-fn-list1-list2) `(fn list1 list2)`
-* [-zip](#-zip-list1-list2) `(list1 list2)`
+* [-zip](#-zip-rest-lists) `(&rest lists)`
 * [-first](#-first-pred-list) `(pred list)`
 * [-last](#-last-pred-list) `(pred list)`
 * [-first-item](#-first-item-list) `(list)`
@@ -1088,12 +1088,14 @@ and the elements from `list2` as `other`.
 (--zip-with (concat it " and " other) '("Batman" "Jekyll") '("Robin" "Hyde")) ;; => '("Batman and Robin" "Jekyll and Hyde")
 ```
 
-#### -zip `(list1 list2)`
+#### -zip `(&rest lists)`
 
-Zip the two lists together.  Return the list where elements
-are cons pairs with car being element from `list1` and cdr being
-element from `list2`.  The length of the returned list is the
-length of the shorter one.
+Zip `lists` together.  Group the head of each list, followed by the
+second elements of each list, and so on. The lengths of the returned
+groupings are equal to the length of the shortest input list.
+
+If two lists are provided as arguments, return the groupings as a list
+of cons cells. Otherwise, return the groupings as a list of lists. 
 
 ```cl
 (-zip '(1 2 3) '(4 5 6)) ;; => '((1 . 4) (2 . 5) (3 . 6))
@@ -1667,6 +1669,7 @@ Change `readme-template.md` or `examples-to-docs.el` instead.
  - [Emanuel Evans](https://github.com/shosti) contributed `-if-let`, `-when-let` and `-insert-at`.
  - [Johan Andersson](https://github.com/rejeep) contributed `-sum`, `-product` and `-same-items?`
  - [Christina Whyte](https://github.com/kurisuwhyte) contributed `-compose`
+ - [Steve Lamb](https://github.com/steventlamb) contributed an n-ary version of `-zip`
 
 Thanks!
 

dash.el

@@ -796,12 +796,27 @@ The anaphoric form `--zip-with' binds the elements from LIST1 as `it`,
 and the elements from LIST2 as `other`."
   (--zip-with (funcall fn it other) list1 list2))
 
-(defun -zip (list1 list2)
-  "Zip the two lists together.  Return the list where elements
-are cons pairs with car being element from LIST1 and cdr being
-element from LIST2.  The length of the returned list is the
-length of the shorter one."
-  (-zip-with 'cons list1 list2))
+(defun -zip (&rest lists)
+  "Zip LISTS together.  Group the head of each list, followed by the
+second elements of each list, and so on. The lengths of the returned
+groupings are equal to the length of the shortest input list.
+
+If two lists are provided as arguments, return the groupings as a list
+of cons cells. Otherwise, return the groupings as a list of lists. "
+  (let* ((n (-min (-map 'length lists)))
+         (level-lists (-map (-partial '-take n) lists))
+         results)
+    (while (> n 0)
+      (let ((split-lists (-map (-partial '-split-at 1) level-lists)))
+        (setq results (cons (-map 'caar split-lists) results))
+        (setq level-lists (-map 'cadr split-lists))
+        (setq n (1- n))))
+    (setq results (nreverse results))
+    (if (= (length lists) 2)
+        ; to support backward compatability, return
+        ; a cons cell if two lists were provided
+        (--map (cons (car it) (cadr it)) results)
+      results)))
 
 (defun -partial (fn &rest args)
   "Takes a function FN and fewer than the normal arguments to FN,

dev/examples.el

@@ -435,7 +435,9 @@
   (defexamples -zip
     (-zip '(1 2 3) '(4 5 6)) => '((1 . 4) (2 . 5) (3 . 6))
     (-zip '(1 2 3) '(4 5 6 7)) => '((1 . 4) (2 . 5) (3 . 6))
-    (-zip '(1 2 3 4) '(4 5 6)) => '((1 . 4) (2 . 5) (3 . 6)))
+    (-zip '(1 2 3 4) '(4 5 6)) => '((1 . 4) (2 . 5) (3 . 6))
+    (-zip '(1 2 3) '(4 5 6) '(7 8 9)) => '((1 4 7) (2 5 8) (3 6 9))
+    (-zip '(1 2) '(3 4 5) '(6)) => '((1 3 6)))
 
   (defexamples -first
     (-first 'even? '(1 2 3)) => 2

readme-template.md

@@ -174,6 +174,7 @@ Change `readme-template.md` or `examples-to-docs.el` instead.
  - [Emanuel Evans](https://github.com/shosti) contributed `-if-let`, `-when-let` and `-insert-at`.
  - [Johan Andersson](https://github.com/rejeep) contributed `-sum`, `-product` and `-same-items?`
  - [Christina Whyte](https://github.com/kurisuwhyte) contributed `-compose`
+ - [Steve Lamb](https://github.com/steventlamb) contributed an n-ary version of `-zip`
 
 Thanks!