Merge pull request #2694 from MadDeveloper/add-move-function

feat(List): add move function

source/index.js

@@ -139,6 +139,7 @@ export { default as mergeWithKey } from './mergeWithKey';
 export { default as min } from './min';
 export { default as minBy } from './minBy';
 export { default as modulo } from './modulo';
+export { default as move } from './move';
 export { default as multiply } from './multiply';
 export { default as nAry } from './nAry';
 export { default as negate } from './negate';

source/move.js

@@ -0,0 +1,36 @@
+import _curry3 from './internal/_curry3';
+
+/**
+ * Move an item, at index `from`, to index `to`, in a list of elements.
+ * A new list will be created containing the new elements order.
+ *
+ * @func
+ * @memberOf R
+ * @category List
+ * @sig Number -> Number -> [a] -> [a]
+ * @param {Number} from The source index
+ * @param {Number} to The destination index
+ * @param {Array} list The list which will serve to realise the move
+ * @return {Array} The new list reordered
+ * @example
+ *
+ *      R.move(0, 2, ['a', 'b', 'c', 'd', 'e', 'f']); //=> ['b', 'c', 'a', 'd', 'e', 'f']
+ *      R.move(-1, 0, ['a', 'b', 'c', 'd', 'e', 'f']); //=> ['f', 'a', 'b', 'c', 'd', 'e'] list rotation
+ */
+var move = _curry3(function(from, to, list) {
+  var length = list.length;
+  var result = list.slice();
+  var positiveFrom = from < 0 ? length + from : from;
+  var positiveTo = to < 0 ? length + to : to;
+  var item = result.splice(positiveFrom, 1);
+
+  return positiveFrom < 0 || positiveFrom >= list.length
+      || positiveTo   < 0 || positiveTo   >= list.length
+    ? list
+    : []
+      .concat(result.slice(0, positiveTo))
+      .concat(item)
+      .concat(result.slice(positiveTo, list.length));
+});
+
+export default move;

test/move.js

@@ -0,0 +1,22 @@
+var R = require('../source');
+var eq = require('./shared/eq');
+
+var list = ['a', 'b', 'c', 'd', 'e', 'f'];
+
+describe.only('move', function() {
+  it('moves an element from an index to another', function() {
+    eq(R.move(0, 1, list), ['b', 'a', 'c', 'd', 'e', 'f']);
+    eq(R.move(2, 1, list), ['a', 'c', 'b', 'd', 'e', 'f']);
+    eq(R.move(-1, 0, list), ['f', 'a', 'b', 'c', 'd', 'e']);
+    eq(R.move(0, -1, list), ['b', 'c', 'd', 'e', 'f', 'a']);
+  });
+
+  it('does nothing when indexes are outside the list outbounds', function() {
+    eq(R.move(-20, 2, list), list);
+    eq(R.move(20, 2, list), list);
+    eq(R.move(2, 20, list), list);
+    eq(R.move(2, -20, list), list);
+    eq(R.move(20, 20, list), list);
+    eq(R.move(-20, -20, list), list);
+  });
+});