我想最多四舍五入两位小数,但只有在必要时。
输入:
10
1.7777777
9.1
输出:
10
1.78
9.1
如何在JavaScript中执行此操作?
我想最多四舍五入两位小数,但只有在必要时。
输入:
10
1.7777777
9.1
输出:
10
1.78
9.1
如何在JavaScript中执行此操作?
当前回答
这里找到的答案都不正确。臭柴塞曼要求四舍五入,但你们都四舍五进。
要进行汇总,请使用以下命令:
Math.ceil(num * 100)/100;
其他回答
我只是想根据前面提到的答案分享我的方法:
让我们创建一个函数,将任何给定的数值舍入到给定的小数位数:
function roundWDecimals(n, decimals) {
if (!isNaN(parseFloat(n)) && isFinite(n)) {
if (typeof(decimals) == typeof(undefined)) {
decimals = 0;
}
var decimalPower = Math.pow(10, decimals);
return Math.round(parseFloat(n) * decimalPower) / decimalPower;
}
return NaN;
}
并为数字原型引入一种新的“舍入”方法:
Object.defineProperty(Number.prototype, 'round', {
enumerable: false,
value: function(decimals) {
return roundWDecimals(this, decimals);
}
});
您可以测试它:
函数舍入WDecimals(n,小数){if(!isNaN(parseFloat(n))&&isFinite(n){if(typeof(小数)==typeof(未定义)){小数=0;}var decimalPower=数学.pow(10,小数);return Math.round(parseFloat(n)*decimalPower)/decimalPower;}返回NaN;}Object.defineProperty(Number.prototype,'round'{可枚举:false,值:函数(小数){返回舍入WDecimals(this,小数);}});var舍入=[{num:10,小数:2},{num:1.7777777,小数:2},{num:9.1,小数:2},{num:55.55,小数:1},{num:55.549,小数:1},{num:55,小数:0},{num:54.9,小数:0},{num:-55.55,小数:1},{num:-55.551,小数:1},{num:-55,小数:0},{num:1.005,小数:2},{num:1.005,小数:2},{num:198000000007,小数:2},],table='<table border=“1”><tr><th>Num</th><th>小数</th><th>结果</th></tr>';$.each(roundables,function(){表+='<tr>'+“<td>”+此.num+“</td>”+“<td>”+此小数+“</td>”+'<td>'+this.num.round(this.decimals)+'</td>'+'</tr>';});table+=“</table>”;$('.results').append(表);<script src=“https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js“></script><div class=“results”></div>
我在MDN上找到了这个。他们的方法避免了前面提到的1.005的问题。
函数roundToTwo(num){return+(数学舍入(num+“e+2”)+“e-2”);}console.log(“1.005=>”,roundToTwo(1.005));console.log('10=>',roundToTwo(10));console.log('1.7777777=>',roundToTwo(1.7777777));console.log('9.1=>',roundToTwo(9.1));console.log('1234.5678=>',roundToTwo(1234.5678));
这里有一个简单的方法:
Math.round(value * 100) / 100
不过,您可能需要继续创建一个单独的函数来为您执行此操作:
function roundToTwo(value) {
return(Math.round(value * 100) / 100);
}
然后,只需传入值。
通过添加第二个参数,可以将其增强为任意小数位数。
function myRound(value, places) {
var multiplier = Math.pow(10, places);
return (Math.round(value * multiplier) / multiplier);
}
将类型保留为整数,以便以后进行排序或其他算术运算:
Math.round(1.7777777 * 100)/100
1.78
// Round up!
Math.ceil(1.7777777 * 100)/100
1.78
// Round down!
Math.floor(1.7777777 * 100)/100
1.77
或转换为字符串:
(1.7777777).toFixed(2)
"1.77"
我的解决方案将输入视为字符串,并使用n位数字的“数学舍入”算法:取n位数字,如果数字n+1等于或大于5,则加1。它还允许指定负数,例如,将123.45舍入为-1的数字为120。它也适用于科学符号(例如1.2e-3)。我没有测量它的速度,我认为这不是最好的表现。
function safeRound( numInput, numPrecision ) {
const strNumber = numInput.toString().replace( 'E', 'e' );
const bSign = '+-'.indexOf( strNumber[ 0 ] ) !== -1;
const strSign = bSign ? strNumber[ 0 ] : '';
const numSign = strSign !== '-' ? +1 : -1;
const ixExponent = ( ixFound => ixFound !== -1 ? ixFound : strNumber.length )( strNumber.indexOf( 'e' ) );
const strExponent = strNumber.substr( ixExponent + 1 );
const numExponent = ixExponent !== strNumber.length ? Number.parseInt( strExponent ) : 0;
const ixDecimal = ( ixFound => ixFound !== -1 ? ixFound : ixExponent )( strNumber.indexOf( '.' ) );
const strInteger = strNumber.substring( !bSign ? 0 : 1, ixDecimal );
const strFraction = strNumber.substring( ixDecimal + 1, ixExponent );
const numPrecisionAdjusted = numPrecision + numExponent;
const strIntegerKeep = strInteger.substring( 0, strInteger.length + Math.min( 0, numPrecisionAdjusted ) ) + '0'.repeat( -Math.min( 0, numPrecisionAdjusted ) );
const strFractionKeep = strFraction.substring( 0, Math.max( 0, numPrecisionAdjusted ) );
const strRoundedDown = strSign + ( strIntegerKeep === '' ? '0' : strIntegerKeep ) + ( strFractionKeep === '' ? '' : '.' + strFractionKeep ) + ( strExponent === '' ? '' : 'e' + strExponent );
const chRoundUp = 0 <= numPrecisionAdjusted ? strFraction.substr( numPrecisionAdjusted, 1 ) : ( '0' + strInteger ).substr( numPrecisionAdjusted, 1 );
const bRoundUp = '5' <= chRoundUp && chRoundUp <= '9';
const numRoundUp = bRoundUp ? numSign * Math.pow( 10, -numPrecision ) : 0;
return Number.parseFloat( strRoundedDown ) + numRoundUp;
}
function safeRoundTest( numInput, numPrecision, strExpected ) {
const strActual = safeRound( numInput, numPrecision ).toString();
const bPassed = strActual === strExpected;
console.log( 'numInput', numInput, 'numPrecision', numPrecision, 'strExpected', strExpected, 'strActual', strActual, 'bPassed', bPassed );
return bPassed ? 0 : 1;
}
function safeRoundTests() {
let numFailed = 0;
numFailed += safeRoundTest( 0, 0, '0' );
numFailed += safeRoundTest( '0', 0, '0' );
numFailed += safeRoundTest( '0.1', 0, '0' );
numFailed += safeRoundTest( '+0.1', 0, '0' );
numFailed += safeRoundTest( '-0.1', 0, '0' );
numFailed += safeRoundTest( '0.1', 1, '0.1' );
numFailed += safeRoundTest( '+0.1', 1, '0.1' );
numFailed += safeRoundTest( '-0.1', 1, '-0.1' );
numFailed += safeRoundTest( '0.9', 0, '1' );
numFailed += safeRoundTest( '+0.9', 0, '1' );
numFailed += safeRoundTest( '-0.9', 0, '-1' );
numFailed += safeRoundTest( '0.9', 1, '0.9' );
numFailed += safeRoundTest( '+0.9', 1, '0.9' );
numFailed += safeRoundTest( '-0.9', 1, '-0.9' );
numFailed += safeRoundTest( '0.5', 0, '1' );
numFailed += safeRoundTest( '+0.5', 0, '1' );
numFailed += safeRoundTest( '-0.5', 0, '-1' );
numFailed += safeRoundTest( '0.4999', 0, '0' );
numFailed += safeRoundTest( '+0.4999', 0, '0' );
numFailed += safeRoundTest( '-0.4999', 0, '0' );
numFailed += safeRoundTest( '1.005', 2, '1.01' );
numFailed += safeRoundTest( '1.00499999999', 2, '1' );
numFailed += safeRoundTest( '012.3456', -4, '0' );
numFailed += safeRoundTest( '012.3456', -3, '0' );
numFailed += safeRoundTest( '012.3456', -2, '0' );
numFailed += safeRoundTest( '012.3456', -1, '10' );
numFailed += safeRoundTest( '012.3456', 0, '12' );
numFailed += safeRoundTest( '012.3456', 1, '12.3' );
numFailed += safeRoundTest( '012.3456', 2, '12.35' );
numFailed += safeRoundTest( '012.3456', 3, '12.346' );
numFailed += safeRoundTest( '012.3456', 4, '12.3456' );
numFailed += safeRoundTest( '012.3456', 5, '12.3456' );
numFailed += safeRoundTest( '12.', 0, '12' );
numFailed += safeRoundTest( '.12', 2, '0.12' );
numFailed += safeRoundTest( '0e0', 0, '0' );
numFailed += safeRoundTest( '1.2e3', 0, '1200' );
numFailed += safeRoundTest( '1.2e+3', 0, '1200' );
numFailed += safeRoundTest( '1.2e-3', 0, '0' );
numFailed += safeRoundTest( '1.2e-3', 3, '0.001' );
numFailed += safeRoundTest( '1.2e-3', 4, '0.0012' );
numFailed += safeRoundTest( '1.2e-3', 5, '0.0012' );
numFailed += safeRoundTest( '+12.', 0, '12' );
numFailed += safeRoundTest( '+.12', 2, '0.12' );
numFailed += safeRoundTest( '+0e0', 0, '0' );
numFailed += safeRoundTest( '+1.2e3', 0, '1200' );
numFailed += safeRoundTest( '+1.2e+3', 0, '1200' );
numFailed += safeRoundTest( '+1.2e-3', 0, '0' );
numFailed += safeRoundTest( '+1.2e-3', 3, '0.001' );
numFailed += safeRoundTest( '+1.2e-3', 4, '0.0012' );
numFailed += safeRoundTest( '+1.2e-3', 5, '0.0012' );
numFailed += safeRoundTest( '-12.', 0, '-12' );
numFailed += safeRoundTest( '-.12', 2, '-0.12' );
numFailed += safeRoundTest( '-0e0', 0, '0' );
numFailed += safeRoundTest( '-1.2e3', 0, '-1200' );
numFailed += safeRoundTest( '-1.2e+3', 0, '-1200' );
numFailed += safeRoundTest( '-1.2e-3', 0, '0' );
numFailed += safeRoundTest( '-1.2e-3', 3, '-0.001' );
numFailed += safeRoundTest( '-1.2e-3', 4, '-0.0012' );
numFailed += safeRoundTest( '-1.2e-3', 5, '-0.0012' );
numFailed += safeRoundTest( '9876.543e210', 0, '9.876543e+213' );
numFailed += safeRoundTest( '9876.543e210', -210, '9.877e+213' );
numFailed += safeRoundTest( '9876.543e210', -209, '9.8765e+213' );
numFailed += safeRoundTest( '9876.543e+210', 0, '9.876543e+213' );
numFailed += safeRoundTest( '9876.543e+210', -210, '9.877e+213' );
numFailed += safeRoundTest( '9876.543e+210', -209, '9.8765e+213' );
numFailed += safeRoundTest( '9876.543e-210', 213, '9.876543e-207' );
numFailed += safeRoundTest( '9876.543e-210', 210, '9.877e-207' );
numFailed += safeRoundTest( '9876.543e-210', 211, '9.8765e-207' );
console.log( 'numFailed', numFailed );
}
safeRoundTests();