Question

（重新发布，因为我以前的帖子由于某种原因无法被提升）我目前有一个脚本，它从文本区域获取数字并使用它们进行各种计算。我的标准偏差函数有问题，因为它不会输出值，即使它的类型是数字，也是正数（.56）。

当我运行此代码时

var variance = findVariance(array);
    variance = parseFloat(variance);
    alert(typeof variance);

结果是

号

值为.56（我知道，因为当我不使用parseFloat时，它返回.56作为字符串）。所以当我运行这段代码时，我感到很困惑

alert("variance " + variance);
alert("sd" + Math.sqrt(variance));

并且两个警报都返回

NaN

这是创建textarea的代码，调用函数processData（它将myTextArea的输入收集到一个数组中，然后调用函数findStandardDeviation）如果你愿意，我也可以发布方差函数。

<textarea id="myTextArea" rows = "7" cols = "50"></textarea><br>

<button onclick="processData()">Done</button>

<p id = "sd"></p>

<script type = "text/javascript">

    var standard_deviation = 0;

    var sdOutput = document.getElementById('sd'); 

function processData()
{
    var arrayOfLines = document.getElementById('myTextArea').value.split('\n');


    findStandardDeviation(arrayOfLines);
}

以下是我简化的剧本：

<script type = "text/javascript">
		
		var mean = 0;
		var median = 0;
		var count = length;
		var mode = 0;
	
		var standard_deviation = 0;

		var meanOutput = document.getElementById('mean'); 
		var countOutput = document.getElementById('count'); 
		var sumOutput = document.getElementById('sum'); 
		var varianceOutput = document.getElementById('variance'); 
		var sdOutput = document.getElementById('sd'); 

	function processData()
	{
		var arrayOfLines = document.getElementById('myTextArea').value.split('\n');

		var sum = findSum(arrayOfLines);
		findMeanOutput(arrayOfLines, sum);
		findVariance(arrayOfLines);
		findStandardDeviation(arrayOfLines);
	}

	function findSum (array)
	{
		var count = array.length;
		var sum = 0;

		for (var a = 0; a < array.length; a++)
		{
			sum += parseInt(array[a]);
		}
		
		countOutput.innerHTML = "Count: " + array.length; 
		sumOutput.innerHTML = "Sum: " + JSON.stringify(sum); 
		sum = parseInt(sum);
		return sum;
	}

	function findMean (array) //Used for finding mean and then returning it
	{
		var sum = 0;

		for(var a = 0; a < array.length; a++)
		{
			sum += parseFloat(array[a]);
		}

		mean = sum/array.length;
		return mean; 
	}

	function findMeanOutput (array, sum) //finds mean and then establishes it as the mean for users input
	{
		mean = sum/array.length;
		meanOutput.innerHTML = "Mean: " +  mean; 
	}

	

	function findVariance (array) 
	{
		var mean = findMean(array);

		var variance = "Variance: " + findMean(array.map(function(num) 
		{
			return Math.pow(num - mean, 2);
		})).toFixed(2);

		varianceOutput.innerHTML = "Variance: " + variance;
		return variance;
	}

	function findStandardDeviation (array) 
	{
		var variance = findVariance(array);
		variance = parseFloat(variance);
		alert(typeof variance);
		alert("variance " + variance);
		alert("sd" + Math.sqrt(variance));
		sdOutput.innerHTML = "Standard Deviation: " + Math.sqrt(variance).toFixed(2); 
	}

</script>

<html>
<head>

</head>
<body>

<p> Please enter a series of numbers, each separated by a new line.<br><p>

<textarea id="myTextArea" rows = "7" cols = "50"></textarea><br>

<button onclick="processData()">Done</button>

<p id = "mean"></p>
<p id = "count"></p>
<p id = "sum"></p>
<p id = "variance"></p>
<p id = "sd"></p>



</body>
</html>

Answer 1

从variance调用返回的

findVariance()变量包含字符串"Variance: "。您可以使用.match()与RegExp /[\d.]+/匹配数字或数字后跟"."后跟数字字符串和+运算符以将字符串转换为数字

var mean = 0;
var median = 0;
var count = length;
var mode = 0;

var standard_deviation = 0;

var meanOutput = document.getElementById('mean');
var countOutput = document.getElementById('count');
var sumOutput = document.getElementById('sum');
var varianceOutput = document.getElementById('variance');
var sdOutput = document.getElementById('sd');

function processData() {
  var arrayOfLines = document.getElementById('myTextArea').value.split('\n');

  var sum = findSum(arrayOfLines);
  findMeanOutput(arrayOfLines, sum);
  findVariance(arrayOfLines);
  findStandardDeviation(arrayOfLines);
}

function findSum(array) {
  var count = array.length;
  var sum = 0;

  for (var a = 0; a < array.length; a++) {
    sum += parseInt(array[a]);
  }

  countOutput.innerHTML = "Count: " + array.length;
  sumOutput.innerHTML = "Sum: " + JSON.stringify(sum);
  sum = parseInt(sum);
  return sum;
}

function findMean(array) //Used for finding mean and then returning it
{
  var sum = 0;

  for (var a = 0; a < array.length; a++) {
    sum += parseFloat(array[a]);
  }

  mean = sum / array.length;
  return mean;
}

function findMeanOutput(array, sum) //finds mean and then establishes it as the mean for users input
{
  mean = sum / array.length;
  meanOutput.innerHTML = "Mean: " + mean;
}



function findVariance(array) {
  var mean = findMean(array);

  var variance = "Variance: " + findMean(array.map(function(num) {
    return Math.pow(num - mean, 2);
  })).toFixed(2);
  varianceOutput.innerHTML = "Variance: " + variance;
  return variance;
}

function findStandardDeviation(array) {
  var variance = findVariance(array);
  variance = parseFloat(+variance.match(/[\d.]+/)[0]);
  console.log(variance);
  alert(typeof variance);
  alert(`variance ${variance}`);
  alert(`sd ${Math.sqrt(variance)}`);
  sdOutput.innerHTML = "Standard Deviation: " + Math.sqrt(variance).toFixed(2);
}

<html>

<head>

</head>

<body>

  <p> Please enter a series of numbers, each separated by a new line.<br>
    <p>

      <textarea id="myTextArea" rows="7" cols="50"></textarea><br>

      <button onclick="processData()">Done</button>

      <p id="mean"></p>
      <p id="count"></p>
      <p id="sum"></p>
      <p id="variance"></p>
      <p id="sd"></p>



</body>

</html>

JS。无法使用alert（）

1 个答案: