_.combine

docs/index.html

@@ -20,6 +20,9 @@ <h3>Iterator Functions</h3>
           <li>
             <a href='#map'>map</a>
           </li>
+          <li>
+            <a href='#combine'>combine</a>
+          </li>
           <li>
             <a href='#each'>each</a>
           </li>
@@ -222,6 +225,14 @@ <h3>Iterator Functions</h3>
           <p class='description'>Produces a new array by mapping each value in iter through a transformation function.</p>
           <pre class='example'>_.map({1,2,3}, function(i) return i*2 end)&#x000A;=> { 2,4,6 }</pre>
         </div>
+        <div class='function' id='combine'>
+          <p>
+            <strong class='name'>combine</strong>
+            <code>_.combine(iters, func)</code>
+          </p>
+          <p class='description'>Produces a new array by mapping each value in each array in iters through a transformation function.</p>
+          <pre class='example'>_.combine({ {1,2,3}, {3,2,1}, {1,1,1} }, function(a,b,c) a+b+c end)&#x000A;=> { 5,5,5 }&#x000A;_.combine({ {3,2,1}, {1,1,1,1,1} }, function(a,b) a+b end)&#x000A;=> { 4,3,2 }</pre>
+        </div>
         <div class='function' id='each'>
           <p>
             <strong class='name'>each</strong>

lib/underscore.lua

@@ -97,6 +97,18 @@ function Underscore.funcs.map(list, func)
 	return mapped
 end
 
+function Underscore.funcs.combine(list, func)
+	local mapped = {}
+	local remaining_lists = _.map(_.rest(list), Underscore.iter)
+	for v1 in Underscore.iter(list[1]) do
+		local remaining_vals = _.map(remaining_lists, function (x)
+			return x()
+		end)
+		mapped[#mapped+1] = func(v1, unpack(remaining_vals))
+	end
+	return mapped
+end
+
 function Underscore.funcs.reduce(list, memo, func)	
 	for i in Underscore.iter(list) do
 		memo = func(memo, i)

spec/combine_spec.lua

@@ -0,0 +1,15 @@
+require 'spec_helper'
+
+describe["_.combine"] = function()
+	before = function()
+		input = { {1,2,3}, {3,2,1,0}, {1,1,1,1,1} }
+		result = _.combine(input, function(a,b,c) return a+b+c end)
+	end
+
+	it["should return an array of size of the first array with the elements of all arrays transformed by the function"] = function()
+		expect(result).should_equal {5,5,5}
+	end
+end
+
+
+spec:report(true)

template/functions.yaml

@@ -13,6 +13,18 @@ iterator_functions:
         _.map({1,2,3}, function(i) return i*2 end)
         => { 2,4,6 }
 
+    - name:
+        combine
+      params:
+        iters, func
+      description:
+        Produces a new array by mapping each value in each array in iters through a transformation function.
+      example: |
+        _.combine({ {1,2,3}, {3,2,1}, {1,1,1} }, function(a,b,c) a+b+c end)
+        => { 5,5,5 }
+        _.combine({ {3,2,1}, {1,1,1,1,1} }, function(a,b) a+b end)
+        => { 4,3,2 }
+
     - name: 
         each
       aliases: