Mapreduce Reduce不是按键计数

我正在使用couchbase 3.0并处理啤酒样本数据

我已创建了一个视图，其地图为：

function (doc, meta) {
  if (doc.category && doc.abv) {
    emit(doc.category, doc.abv);
  }
}

这将提供以下输出：

{"total_rows":2397,"rows":[
{"id":"21st_amendment_brewery_cafe-watermelon_wheat","key":"Belgian and French Ale","value":5.5},
{"id":"3_fonteinen_brouwerij_ambachtelijke_geuzestekerij-drie_fonteinen_kriek","key":"Belgian and French Ale","value":5},
{"id":"3_fonteinen_brouwerij_ambachtelijke_geuzestekerij-oude_geuze","key":"Belgian and French Ale","value":6},
{"id":"512_brewing_company-512_wit","key":"Belgian and French Ale","value":5.2},
{"id":"512_brewing_company-one","key":"Belgian and French Ale","value":8},
{"id":"abbaye_de_maredsous-10","key":"Belgian and French Ale","value":10},
{"id":"abbaye_de_maredsous-8","key":"Belgian and French Ale","value":8},
{"id":"abbaye_notre_dame_du_st_remy-rochefort_10","key":"Belgian and French Ale","value":11.3},
{"id":"abita_brewing_company-satsuma_harvest_wit","key":"Belgian and French Ale","value":5.1},
{"id":"affligem_brouwerij-affligem_dubbel","key":"Belgian and French Ale","value":6.8}
]
}

选择前10名时

现在我想数一数每类啤酒的数量。因此，我决定添加内置的reduce

\u count

不幸的是，输出不是预期的，而是：

{"rows":[
 {"key":null,"value":2397}
 ]
}

---

为什么我的key设置为null，而不是

文档类别

？

我意识到我在查询视图时忘记了添加group参数。有了它，一切都很好