javascript - 按国家数量对各大洲进行排序

Question

我有一个国家/地区列表:

"country": [
       {
           "countryCode": "AD",
           "countryName": "Andorra",
           "currencyCode": "EUR",
           "population": "84000",
           "capital": "Andorra la Vella",
           "continentName": "Europe",
           "continent": "EU",
           "areaInSqKm": "468.0",
           "languages": [
               "ca"
           ]
       },
       {
           "countryCode": "AE",
           "countryName": "United Arab Emirates",
           "currencyCode": "AED",
           "population": "4975593",
           "capital": "Abu Dhabi",
           "continentName": "Asia",
           "continent": "AS",
           "areaInSqKm": "82880.0",
           "languages": [
               "ar-AE",
               "fa",
               "en",
               "hi",
               "ur"
           ]
       },
etc.

现在我必须用 JSON 编写一个 Map/Reduce 函数才能获得如下输出:

键:Afrika 值:xxx键:亚洲 值:xxx等等

其中“值”代表每个大陆的国家/地区数量。

我已经尝试过这个 map 功能:

function(doc) {
   var a
   {
      for (a in doc.country){
         emit(doc.country[a].continentName, 1)
      };
   }
}

Answer 1

map 功能:

function(doc) {
    var country = doc.country;
    var i;
        for (i in country) {
            emit (country[i].continentName, 1)
        };
}

然后你必须使用Reduce Function来减少它:

function(keys, values) {
   return sum(values);}