如何使用javascript從每個JSON對象中提取特定屬性

Question

我有一個JSON數據集

[{"key":"Albania",
    "values":[{                                                                  
        "Country_Names":"Albania",
        "Total":"3.8",
        "Change_total":"-38.7",
        "Main activity electricity and heat production":"0.1",
        "Main activity electricity plants":"","Main activity CHP plants":"",
        "Unallocated autoproducers / Other energy industry own use":"0.1",
        "Other":"1.4",
        "Manufacturing industries and construction":"1",
        "Iron and steel":"0","Chemical and petrochemical":"0","Machinery":"",
        "Mining and quarrying":"",
        "Food and tobacco":"0.1",
        "Paper, pulp and printing":"",
        "Construction":"0",
        "Transport":"2.2",
        "Road":"2.2",
        "Domestic aviation":"",
        "Rail":"0",
        "Domestic navigation":"0.1",
        "Residential":"0.2",
        "Commercial and public services":"0",
        "Agriculture/forestry":"0.2",
        "Sub-bituminous coal / Lignite":"",
        "Other bituminous coal":"",
        "Natural gas":"0",
        "Motor gasoline excl. bio":"0.3",
        "Gas/diesel oil excl. bio":"2.2"
    }]
}]

我想從每個鍵（國家/地區）中提取特定值（例如Road，Rail），並從每個對象中繪制一個單獨的餅圖。 例如，阿爾巴尼亞的一個圖表顯示了道路和鐵路價值，然后是數據集中下一個國家的相同圖表。

我試圖通過以下代碼實現此目的：

function checkIt(data) {
    var countriesByName = d3.nest()
    .key(function(d) { return d.Country_Names; })
    .entries(data);
    //console.log(countriesByName)
    var data = JSON.stringify(countriesByName);
    console.log(data);
    function makePie() {
        function myfunc(data){
            var obj =  [];
            for (var i in data.key) {
                obj.push('Road' + m.countriesByName[i].key.values[i].Food+ ' and tobacco');
            }
        }
        var data1 =  myfunc(data);
        //console.log(data)
        var chart = c3.generate({
            bindto: "#left",
            data: {
                columns: [
                data1
                ],type : "donut" 
            }
        });
    }
    makePie();
};
d3.json("https://gist.githubusercontent.com/heenaI/cbbc5c5f49994f174376/raw/82cd19eff7db367193cf8ce00144a40ea8d140ac/data.json", checkIt);

我收到以下錯誤：

未捕獲的TypeError：無法讀取未定義的屬性“0”

這是數據集的JS小提琴 ：

預期的結果是這樣的[“道路”，2.2]然后我想把它作為循環運行數據內的所有國家，以獲得類似的數組

Answer 1

您忘記將json字符串解析為JSONObject，因此您無法從字符串訪問key屬性。

在var data = JSON.stringify(countriesByName); 你必須像這樣解析你的對象：

var data = JSON.parse(data);

完成此操作后，您可以訪問JSONObject屬性。

檢查這個演示 。