在vega-lite中排序标称轴值

Question

我有一个vega-lite分层条形图来比较likert scale前后的调查结果。X轴具有likert选项，但这些选项是按字母顺序排序的。X轴值的顺序可以排序吗？例如“强烈不同意，不同意，神经质，同意，强烈同意”？

vega-lite示例代码：

{
"$schema": "https://vega.github.io/schema/vega-lite/v2.json",
"description": "A bar chart showing the US population distribution of     age groups and gender in 2000.",
"data": { 
  "values": [
    {"type":"pre", "answer":"Strongly Disagree", "total":15},
    {"type":"post", "answer":"Strongly Disagree", "total":30},
    {"type":"pre", "answer":"Disagree", "total":15},
    {"type":"post", "answer":"Disagree", "total":30},
    {"type":"pre", "answer":"Neutral", "total":15},
    {"type":"post", "answer":"Neutral", "total":30},
    {"type":"pre", "answer":"Neutral", "total":15},
    {"type":"post", "answer":"Neutral", "total":30},
    {"type":"pre", "answer":"Agree", "total":15},
    {"type":"post", "answer":"Agree", "total":30},
    {"type":"pre", "answer":"Strongly Agree", "total":20},
    {"type":"post", "answer":"Strongly Agree", "total":40}
  ]
},
"mark": "bar",
"encoding": {
    "x": {
      "field": "answer", "type": "nominal"
    },
    "y": {
      "field": "total", "type": "quantitative",
      "axis": {"title": "% Counts"},
      "stack": "none"
    },
    "color": {
      "field": "type", "type": "nominal",
      "axis": {"title": "Answer"},
      "scale": {"range": ["#e377c2","#1f77b4"]}
    },
    "opacity": {"value": 0.7}
}
}