在PHP中将数字格式设置为N个有效数字 [英] Format number to N significant digits in PHP

问题描述

我想格式化(四舍五入)浮点(双精度)数字，例如，这样说2个有效数字:

I would like to format (round) float (double) numbers to lets say 2 significant digits for example like this:

1        => 1
11       => 11
111      => 110
119      => 120
0.11     => 0.11
0.00011  => 0.00011
0.000111 => 0.00011

所以任意精度保持不变

我希望它已经内置了一些不错的功能，但到目前为止找不到任何功能

I expect there is some nice function for it already built in, but could not find any so far

有人指出我如何四舍五入下降到php中最接近的有效数字，该数字很接近，但不适用于N个有效数字，我不确定0.000XXX数字有什么作用

I was pointed to How to round down to the nearest significant figure in php, which is close but doesn't work for N significant digits and I'm not sure what it does with 0.000XXX numbers

推荐答案

要将数字四舍五入为n个有效数字，您需要找到数字的大小(以10的幂为单位)，然后从n中减去.

To get a number rounded to n significant figures you need to find the size of the number in powers of ten, and subtract that from n.

这对于简单的四舍五入非常有用:

This works fine for simple rounding:

function sigFig($value, $digits)
{
    if ($value == 0) {
        $decimalPlaces = $digits - 1;
    } elseif ($value < 0) {
        $decimalPlaces = $digits - floor(log10($value * -1)) - 1;
    } else {
        $decimalPlaces = $digits - floor(log10($value)) - 1;
    }

    $answer = round($value, $decimalPlaces);
    return $answer;
}

这将给出以下内容:
0.0001234567返回0.0001235
123456.7返回123500

This will give the following:
0.0001234567 returns 0.0001235
123456.7 returns 123500

但是，例如10到4个有效数字之类的值应严格表示为10.00，以表示该值的精确度.

However a value such as 10 to four significant figures should strictly be represented as 10.00 to signify the precision to which the value is known.

如果这是所需的输出，则可以使用以下内容:

If this is the desired output you can use the following:

function sigFig($value, $digits)
{
    if ($value == 0) {
        $decimalPlaces = $digits - 1;
    } elseif ($value < 0) {
        $decimalPlaces = $digits - floor(log10($value * -1)) - 1;
    } else {
        $decimalPlaces = $digits - floor(log10($value)) - 1;
    }

    $answer = ($decimalPlaces > 0) ?
        number_format($value, $decimalPlaces) : round($value, $decimalPlaces);
    return $answer;
}

现在1显示为1.000

Now 1 is displayed as 1.000

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