Sort characters to always return same mapping

play_char.ipynb

@@ -59,7 +59,7 @@
     "class CharDataset(Dataset):\n",
     "\n",
     "    def __init__(self, data, block_size):\n",
-    "        chars = list(set(data))\n",
+    "        chars = sorted(list(set(data)))\n",
     "        data_size, vocab_size = len(data), len(chars)\n",
     "        print('data has %d characters, %d unique.' % (data_size, vocab_size))\n",
     "        \n",