implements the key_by utility function

src/array/init.lua

@@ -652,6 +652,20 @@ array = {
     local mapped = array.map(obj, callback)
 
     return array.flat(mapped)
+  end,
+
+  -- Creates a new table composed of keys generated from the results of running each element of the given table through the given callback
+  -- @param obj {table}
+  -- @param callback {function}
+  -- @return {table}
+  key_by = function(obj, callback)
+    utils.raises_error(array, obj, 'key_by')
+
+    return array.reduce(obj, function(accumulator, current)
+      local key = callback(current)
+      accumulator[key] = current
+      return accumulator
+    end, {})
   end
 }
 

test.lua

@@ -434,3 +434,15 @@ test('flat_map', function(a)
     { 1, 2, 2, 4, 3, 6 }
   )
 end)
+
+test('key_by', function(a)
+  a.deep_equal(
+    array.key_by({ { id = 1, name = 'lua' }, { id = 2, name = 'javascript' } }, function(item)
+      return item.id
+    end),
+    {
+      [1] = { id = 1, name = 'lua' },
+      [2] = { id = 2, name = 'javascript' }
+    }
+  ) 
+end)