Question

我有一个对象数组，我想获得最大created_on值。

我试试这段代码：

receipt_details

created_on

但结果是receipt_details而非created_on。

我不必使用d3功能，即使纯粹的javascript也没问题。

Answer 1

您的'NaN'是字符串，而不是实际的NaN，但无论如何，您可以在reduce测试时Math.max prevalence：

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var ex=[{"name":"a","prevalence":"NaN"},{"name":"a","prevalence":"5"},{"name":"b","prevalence":"0"},{"name":"a","prevalence":"NaN"},{"name":"c","prevalence":"100"},{"name":"c","prevalence":"20"},{"name":"a","prevalence":"3"}];
const max = Math.max(...ex.reduce(
  (accum, { prevalence }) =>
    isNaN(prevalence) ? accum : [...accum, prevalence],
  [])
);
console.log(max);

＆＃13;

Answer 2

实际上"5"大于"100"，因为它们被比作字符串。您需要确保将它们作为数字进行比较：

return +d.prevalence;

或者您采取稍微宽松的方法：

  const maxPrevalence = Math.max(...ex.map(d => +d.prevalence).filter(p => !isNaN(p)));

Answer 3

您可以在映射的普遍性值上使用Math.max（）：

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adb devices

＆＃13;

Answer 4

您可以使用Array.reduce＆amp; parseInt为了迭代数组，并搜索最大值; parseInt的使用是必需的，因为普遍性是一个字符串。

＆＃13;

const ex = [{
    "name": "a",
    "prevalence": "NaN"
  },
  {
    "name": "a",
    "prevalence": "5"
  },
  {
    "name": "b",
    "prevalence": "0"
  },
  {
    "name": "a",
    "prevalence": "NaN"
  },
  {
    "name": "c",
    "prevalence": "100"
  },
  {
    "name": "c",
    "prevalence": "20"
  },
  {
    "name": "a",
    "prevalence": "3"
  }
];

const result = ex.reduce((max, current) => {
  const prevalence = parseInt(current.prevalence) || 0;
  return max.prevalence > prevalence ? max : current;
}, {
  prevalence: '0'
});

console.log(result);

＆＃13;

Answer 5

使用d3.js，此代码有效。 Number("100")为100，Number('NaN')为NaN。

// max of selected vaccine
var ex = [{"name": "a", "prevalence": "NaN"}, {"name": "a", "prevalence": "5"}, {"name": "b", "prevalence": "0"}, {"name": "a", "prevalence": "NaN"}, {"name": "c", "prevalence": "100"}, {"name": "c", "prevalence": "20"}, {"name": "a", "prevalence": "3"}];

var maxPrevalence = d3.max(ex, function(d) { return Number(d.prevalence) });
console.log('\nmaxPrevalence:', maxPrevalence);

<script src='https://d3js.org/d3.v5.js' charset='utf-8'></script>

在包含NaN值的对象数组中查找最大值

5 个答案: