根据属性计算对象中的项目总数

Question

Business =  {
  1: { Country: "France" },
  2: { Country: "France" },
  3: { Country: "UnitedKingdom" },
  4: { Country: "France" }
}

我有一个企业对象列表（分配了一个ID），每个企业都有自己的国家。

我的问题是通过财产寻找金额的最佳方法是什么？ 例如，如果我想查找法国企业的总数，则根据代码示例将返回3。

Answer 1

您可以尝试这样的事情：

 var Business = { 1: {Country:"France"} , 2: {Country:"United Kingdom"} , 3: {Country:"France"} , 4: {Country:"France"} }; var businessInFrance = Object.keys(Business) .map(key => Business[key]) .reduce(function(acc, val){ return val.Country === "France" ? acc+=1 : acc; },0); console.log(businessInFrance); 

• Object.keys(Business)返回一个数组，其中包含Business拥有的枚举
• map将传递给上一步的函数应用到函数，并返回一个新数组。 该数组的元素是业务的价值
• reduce对上一步数组的每个元素应用传递的函数，当Country属性的值等于“ France”时，我们将累加器acc的值加1，否则将其返回不变。 然后，返回累加器的值。

Answer 2

您的对象有问题。 您可以使用以下内容，但我不得不问为什么不只使用数组？

Business = {
  01: {Country:"France"},
  02: {Country:"United Kingdom"},
  03: {Country:"France"},
  04: {Country:"France"},
}

 const BusinessArray = [ {Country:"France"}, {Country:"United Kingdom"}, {Country:"France"}, {Country:"France"}, ] console.log( BusinessArray.filter(x => x.Country === 'France').length ) 

 Business = { 01: {Country:"France"}, 02: {Country:"United Kingdom"}, 03: {Country:"France"}, 04: {Country:"France"}, } const countriesCount = (country, businesses) => Object.keys(businesses) .filter(x => businesses[x].Country === country) .length console.log( countriesCount('France', Business), countriesCount('United Kingdom', Business) ) 

Answer 3

您可以使用一个对象来计数国家。

 var business = { 1: { Country: "France" }, 2: { Country: "France" }, 3: { Country: "UnitedKingdom" }, 4: { Country: "France" } }, count = Object.keys(business).reduce(function (r, k) { var country = business[k].Country; r[country] = (r[country] || 0) + 1; return r; }, Object.create(null)); console.log(count.France); console.log(count); 

 .as-console-wrapper { max-height: 100% !important; top: 0; } 

Answer 4

首先，您的语法不正确，将导致错误。

如果将所有对象都包含在数组中，则不需要这些对象来维护它们自己的标识符，并且可以很容易地做到这一点：

 var business = [ {country:"France"}, {country:"United Kingdom"}, {country:"France"}, {country:"France"} ]; console.log("The amount of countries is: " + business.length); var count = 0; business.forEach(function(value){ count = (value.country === "France") ? ++count : count; }); console.log("The amount of times France appears is: " + count); 

Answer 5

Object.keys返回对象的键。 您可以遍历键并计算所需的结果。 这是一个例子。

 var Business = { 1:{ Country: "France" }, 2:{ Country: "France" }, 3:{ Country: "UnitedKingdom" }, 4:{ Country: "France" }}; var countByCountry = function(country){ var result = 0; Object.keys(Business).forEach(function(it){ result += (Business[it].Country === country ? 1 : 0); console.log(it, country, result); }); return result; } console.log(countByCountry('France'));