gistfile1.js

{"inputs":{
    "bucket":"invoices",
    "key_filters":[["tokenize", ",", 4],["eq", "key"]]
 },
 "query":[
{"map":
  {
  "language":"javascript",
  "source": "function(value, key, arg) { return [value.key] }",
  "keep": true
  }
}
]}