PHP abs()函数

abs(mixed $num): mixed

<?php
// 整数绝对值
echo abs(-5) . "\n";       // 输出: 5
echo abs(5) . "\n";        // 输出: 5
echo abs(0) . "\n";        // 输出: 0

// 浮点数绝对值
echo abs(-3.14) . "\n";    // 输出: 3.14
echo abs(3.14) . "\n";     // 输出: 3.14
echo abs(-2.5) . "\n";     // 输出: 2.5

// 字符串数字的绝对值
echo abs("-10") . "\n";    // 输出: 10
echo abs("15.75") . "\n";  // 输出: 15.75

// 科学计数法
echo abs(-1.23e4) . "\n";  // 输出: 12300
echo abs(1.23e-4) . "\n";  // 输出: 0.000123

// 检查类型
var_dump(abs(-10));        // 输出: int(10)
var_dump(abs(-3.14));      // 输出: float(3.14)
?>

<?php
// 计算温度变化
$currentTemp = 15.5;
$targetTemp = 20.0;
$tempDifference = abs($currentTemp - $targetTemp);
echo "温度差: " . $tempDifference . "°C\n";  // 输出: 温度差: 4.5°C

// 计算银行账户余额变化
$previousBalance = 1000.00;
$currentBalance = 750.50;
$balanceChange = abs($currentBalance - $previousBalance);
echo "余额变化: $" . $balanceChange . "\n";  // 输出: 余额变化: $249.5

// 计算坐标点距离（一维）
$pointA = 10;
$pointB = -5;
$distance = abs($pointB - $pointA);
echo "点A({$pointA})和点B({$pointB})的距离: " . $distance . "\n";  // 输出: 距离: 15

// 计算时间差
$startTime = 9.5;  // 9:30
$endTime = 15.25;  // 15:15
$hoursWorked = abs($endTime - $startTime);
echo "工作时间: " . $hoursWorked . " 小时\n";  // 输出: 工作时间: 5.75 小时
?>

<?php
// 方法1: 使用array_map
$numbers = [-10, -5.5, 0, 3, 7.2, -2.8];
$absNumbers = array_map('abs', $numbers);
echo "原始数组: " . implode(', ', $numbers) . "\n";
echo "绝对值数组: " . implode(', ', $absNumbers) . "\n";

// 方法2: 使用循环
$data = [-100, -50, 0, 25, 75];
$absoluteData = [];
foreach ($data as $value) {
    $absoluteData[] = abs($value);
}
echo "数据: " . implode(', ', $data) . "\n";
echo "绝对值: " . implode(', ', $absoluteData) . "\n";

// 方法3: 使用array_walk（原地修改）
$values = [-1.5, -2.3, 3.7, -4.1];
echo "修改前: " . implode(', ', $values) . "\n";
array_walk($values, function(&$item) {
    $item = abs($item);
});
echo "修改后: " . implode(', ', $values) . "\n";

// 计算数组中最大负数的绝对值
$negativeNumbers = [-15, -3, -20, -1, -8];
$maxNegative = max($negativeNumbers);
$absMaxNegative = abs($maxNegative);
echo "最大负数: " . $maxNegative . "\n";
echo "其绝对值: " . $absMaxNegative . "\n";
?>

<?php
// 计算平方根前的绝对值（防止负数）
function safeSqrt($number) {
    return sqrt(abs($number));
}

echo "sqrt(abs(-16)) = " . safeSqrt(-16) . "\n";  // 输出: 4
echo "sqrt(abs(16)) = " . safeSqrt(16) . "\n";    // 输出: 4

// 计算两个向量的曼哈顿距离（一维）
function manhattanDistance($point1, $point2) {
    return abs($point1 - $point2);
}

$p1 = 3;
$p2 = -2;
echo "点({$p1})和点({$p2})的曼哈顿距离: " . manhattanDistance($p1, $p2) . "\n";

// 检查数字是否在指定范围内（考虑正负）
function isWithinRange($value, $center, $range) {
    return abs($value - $center) <= $range;
}

$value = 15;
$center = 10;
$range = 6;
echo "值 {$value} 是否在以 {$center} 为中心，{$range} 为半径的范围内: " .
     (isWithinRange($value, $center, $range) ? '是' : '否') . "\n";

// 计算误差率（百分比）
function calculateErrorRate($expected, $actual) {
    if ($expected == 0) {
        return abs($actual) * 100;  // 避免除零错误
    }
    return abs(($actual - $expected) / $expected) * 100;
}

$expectedValue = 100;
$actualValue = 92;
$errorRate = calculateErrorRate($expectedValue, $actualValue);
echo "预期: {$expectedValue}, 实际: {$actualValue}, 误差率: " . round($errorRate, 2) . "%\n";
?>

<?php
// 自定义绝对值函数（支持更多类型）
function customAbs($value) {
    if (is_numeric($value)) {
        return abs($value);
    }

    if (is_string($value)) {
        // 尝试提取字符串中的数字
        if (preg_match('/-?\d+(\.\d+)?/', $value, $matches)) {
            return abs((float)$matches[0]);
        }
    }

    throw new InvalidArgumentException("参数必须是数字或包含数字的字符串");
}

// 测试自定义函数
try {
    echo customAbs(-42) . "\n";               // 42
    echo customAbs("温度: -23.5°C") . "\n";   // 23.5
    echo customAbs("15") . "\n";              // 15
    echo customAbs("abc") . "\n";             // 抛出异常
} catch (Exception $e) {
    echo "错误: " . $e->getMessage() . "\n";
}

// 创建安全的绝对值计算器类
class AbsoluteValueCalculator {
    private $precision;

    public function __construct($precision = 2) {
        $this->precision = $precision;
    }

    public function calculate($value) {
        if (!is_numeric($value)) {
            throw new InvalidArgumentException("输入值必须是数字");
        }

        $result = abs($value);

        // 如果设置精度，四舍五入
        if (is_float($result) && $this->precision !== null) {
            $result = round($result, $this->precision);
        }

        return $result;
    }

    public function calculateArray(array $values) {
        $results = [];
        foreach ($values as $index => $value) {
            try {
                $results[$index] = $this->calculate($value);
            } catch (Exception $e) {
                $results[$index] = null;  // 或抛出异常
            }
        }
        return $results;
    }
}

// 使用计算器
$calculator = new AbsoluteValueCalculator(3);
echo "单个计算: " . $calculator->calculate(-12.34567) . "\n";  // 12.346

$mixedValues = [-5, 3.14159, "-10.5", "无效", 0];
$results = $calculator->calculateArray($mixedValues);
echo "数组计算: " . implode(', ', $results) . "\n";  // 5, 3.142, 10.5, , 0
?>

<?php
// 性能测试：内置abs() vs 条件判断
function absConditional($num) {
    return $num < 0 ? -$num : $num;
}

function absBitwise($num) {
    return $num < 0 ? (~$num + 1) : $num;  // 位运算（仅整数）
}

// 测试性能（示例代码，实际测试需要更多迭代）
$testNumber = -12345.67;
$iterations = 1000000;

$start1 = microtime(true);
for ($i = 0; $i < $iterations; $i++) {
    $result = abs($testNumber);
}
$time1 = microtime(true) - $start1;

$start2 = microtime(true);
for ($i = 0; $i < $iterations; $i++) {
    $result = absConditional($testNumber);
}
$time2 = microtime(true) - $start2;

echo "内置abs()耗时: " . round($time1 * 1000, 2) . "ms\n";
echo "条件判断耗时: " . round($time2 * 1000, 2) . "ms\n";
echo "推荐使用内置abs()函数\n";
?>