I'm trying to create a list of subpaths from a flattened array.

Here's the starting point:

<!-- language: lang-js -->

    var flat = [
      {path: "/"  },
      {path: "A"  },
      {path: "A.A"},
      {path: "A.B"},
      {path: "A.C"},
      {path: "B"  },
      {path: "C"  }
    ]

The goal is that anything under a parent would be a subpath of that.  So the goal would look like this:

<!-- language: lang-js -->

    var goal = [
      {path: "/"  },
      {path: "A",
       subpaths: [
        {path: "A.A"},
        {path: "A.B"},
        {path: "A.C"}
       ]
      },
      {path: "B"  },
      {path: "C"  }
    ]

I've hobbled together a solution, but it doesn't feel very clean and is probably prone to breakage:

<!-- language: lang-js -->

    var nested = [];
    for (var i=0; i < flat.length; i++) {
      // split components up
      var routes = flat[i].path.split(".");
      
      // get parent key
      var key = routes[0];

      // check if we've already added the key
      var index = -1;
      for (var j=0; j < nested.length; j++) {
        if (nested[j].path == key) {
          index = j;
          break;
        }
      }

      if (index===-1) {
        // if we have a new parent add it
        nested.push(flat[i])
        
      } else { 
        // create subpaths property on new object
        if (!nested[index].subpaths) { nested[index].subpaths = [] }
        
        // add child paths to existing parent
        nested[index].subpaths.push(flat[i])
      }
    }

**Here's a working Demo in Stack Snippets**

<!-- begin snippet: js hide: true -->

<!-- language: lang-js -->

    var flat = [
      {path: "/"  },
      {path: "A"  },
      {path: "A.A"},
      {path: "A.B"},
      {path: "A.C"},
      {path: "B"  },
      {path: "C"  }
    ]


    var nested = [];
    for (var i=0; i < flat.length; i++) {
      // split components up
      var routes = flat[i].path.split(".");
      
      // get parent key
      var key = routes[0];

      // check if we've already added the key
      var index = -1;
      for (var j=0; j < nested.length; j++) {
        if (nested[j].path == key) {
          index = j;
          break;
        }
      }
      
      if (index===-1) {
        // if we have a new parent add it
        nested.push(flat[i])
        
      } else { 
        // create subpaths property on new object
        if (!nested[index].subpaths) { nested[index].subpaths = [] }
        
        // add child paths to existing parent
        nested[index].subpaths.push(flat[i])
      }
    }

    console.log(nested);

<!-- end snippet -->

I'm also open to using jQuery or Underscore if they expose any functionality that would tidy up the source code. I'd also like to modify the code so it could handle this recursively with an unspecified level of depth on each node.