Grouping utilities

ObjectHelpers.cs

using UnityEngine;
using UnityEditor;
using System.Linq;
using System;

namespace Feed {
  public static class ObjectHelpers {
    [MenuItem("Feed/Objects/Group parent position %g")]
    public static void GroupSelected() {
      if (!SelectedSiblings(out var selected)) {
        return;
      }

      var parent = selected[0].parent;
      var group = CreateGroupObject(parent);

      ParentAll(group, selected);

      Selection.objects = new [] { group.gameObject };
      // Would be nice to set the object to rename here but it's tricky...
      // see: http://answers.unity.com/answers/940887/view.html
    }

    [MenuItem("Feed/Objects/Group center %#g")]
    public static void GroupCenter() {
      if (!SelectedSiblings(out var selected)) {
        return;
      }

      var parent = selected[0].transform.parent;
      var group = CreateGroupObject(parent);

      group.position = AveragePosition(selected);

      ParentAll(group, selected);

      Selection.objects = new [] { group.gameObject };
    }

    static Vector3 AveragePosition(Transform[] transforms) {
      Vector3 result = transforms[0].transform.position;
      for (var i = 1; i < transforms.Length; i++) {
        result += transforms[i].position;
      }
      return result / transforms.Length;
    }

    static void ParentAll(Transform parent, Transform[] selected) {
      for (var i = 0; i < selected.Length; i++) {
        Undo.SetTransformParent(
          selected[i],
          parent,
          "Set parent"
        );
      }
    }

    static Transform CreateGroupObject(Transform parent) {
      const string name = "New group";
      var group = (parent is RectTransform
        ? new GameObject(name, typeof(RectTransform))
        : new GameObject(name)
      ).transform;
      Undo.RegisterCreatedObjectUndo(group.gameObject, "Create group");

      group.parent = parent;
      group.localPosition = Vector3.zero;
      group.localRotation = Quaternion.identity;
      group.localScale = Vector3.one;

      return group;
    }

    static bool SelectedSiblings(out Transform[] selected) {
      if (SelectedTransforms(out var transforms)) {
        for (var i = 1; i < transforms.Length; i++) {
          if (transforms[i].transform.parent != transforms[0].transform.parent) {
            Debug.LogWarning($"{transforms[0].name} and {transforms[i].name} do not share a parent");
            selected = Array.Empty<Transform>();
            return false;
          }
        }
        selected = transforms;
        return true;
      }
      selected = Array.Empty<Transform>();
      return false;
    }

    public static bool SelectedTransforms(out Transform[] selected) {
      selected = Selection.objects
        .Select(o => o as GameObject)
        .Where(go => go != null)
        .Select(go => go.transform)
        .ToArray();

      if (selected.Length == 0) {
        Debug.LogWarning("Nothing selected");
        selected = Array.Empty<Transform>();
        return false;
      }

      return true;
    }
  }
}