is there a way to round a number 0.005 to down.
For example:
5.425 is to be rounded to 5.42
2.336 is to be rounded to 2.34
0.5556 is to be rounded to 0.56
UPDATE: I don't have always 3 digits after point I can have more than that. like 5.555556, 12.3456789, etc
already tried with parseFloat(number).toFixed(2) but it doesn't really work for some cases, value like 0.555 the output will be 0.56 instead of 0.55
thanks in advance
The issue is, that JavaScript don't know the numbers like 5.425. The floating point implementation of computers and therefor for the most programming languages is binary based and not decimal based (see IEEE 754). So each scanned number is rounded to the nearest possible value first:
5.425 .toPrecision(18); // result "5.42499999999999982" => ToFixed(2)="5.42"
2.336 .toPrecision(18); // result "2.33599999999999985" => ToFixed(2)="2.34"
0.5556 .toPrecision(18); // result "0.555599999999999983" => ToFixed(2)="0.56"
And these scanning results are used for further processing. So the results using toFixed(2) are expected and absolute correct.
And don't believe in other solutions (sometimes called betterToFixed()) to fix this issue. They have issues with other numbers, because many authors don't understand the mathematics behind the scenes.
You've said you want 5.425 to round to 5.42 but that you want 5.555556 to round to 5.556. That means you're doing a round-ties-down (or perhaps round-ties-toward-zero) operation rather than a "normal" round where ties go up (or away from zero, depending).
The only way I can think of to do that is to subtract one from the final digit of the number at each stage of rounding, like this:
// Round the given number to the given number of places, but rounding ties down
// (0.5 rounds to 0 instead of 1, 0.55 rounds to 0.5 instead of 0.6, etc.)
function roundTiesDown(n, places) {
if (places < 1) {
throw new Error(`Received places=${places}, but must be >=1`);
}
let currentPlaces = significantFractionalPlaces(n)
// Round ties down at each level, e.g. (if places = 2):
// 0.55556 => 0.5556
// 0.5556 => 0.556
// 0.556 => 0.56
// and
// 0.55555 => 0.5555 (would be 0.5556 with "normal" rounding)
// 0.5555 => 0.555
// 0.555 => 0.55
while (currentPlaces > places) {
const subtrahend = 1 / Math.pow(10, currentPlaces);
--currentPlaces;
const multiplier = Math.pow(10, currentPlaces);
n = Math.round((n - subtrahend) * multiplier) / multiplier;
}
return n;
}
Live Example:
// Get a function to convert numbers to string without going to scientific notation
let numberToString;
if (typeof Intl === "object" && typeof Intl.NumberFormat === "function") {
// Intl.NumberFormat lets us do this properly
const format = new Intl.NumberFormat(undefined, {
style: "decimal",
useGrouping: false,
maximumFractionDigits: 20
});
numberToString = n => format.format(n);
} else {
// Fall back to toString on platforms without Intl.NumberFormat
// (all major browsers have it, including IE11 -
// https://caniuse.com/#feat=mdn-javascript_builtins_intl_numberformat)
const rexContainsE = /e/i;
numberToString = n => {
const str = n.toString();
if (rexContainsE.test(str)) {
// Went to scientific notation
throw new Error("Can't handle numbers this big on this platform");
}
return str;
};
}
// Get the currentPlaces number of significant places in the given number
function significantFractionalPlaces(n) {
const str = numberToString(n);
const idx = str.indexOf(".");
return idx === -1 ? 0 : str.length - idx - 1;
}
// Round the given number to the given number of places, but rounding ties down
// (0.5 rounds to 0 instead of 1, 0.55 rounds to 0.5 instead of 0.6, etc.)
function roundTiesDown(n, places) {
if (places < 1) {
throw new Error(`Received places=${places}, but must be >=1`);
}
let currentPlaces = significantFractionalPlaces(n)
// Round ties down at each level, e.g. (if places = 2):
// 0.55556 => 0.5556
// 0.5556 => 0.556
// 0.556 => 0.56
// and
// 0.55555 => 0.5555 (would be 0.5556 with "normal" rounding)
// 0.5555 => 0.555
// 0.555 => 0.55
while (currentPlaces > places) {
const subtrahend = 1 / Math.pow(10, currentPlaces);
--currentPlaces;
const multiplier = Math.pow(10, currentPlaces);
/* For your real function, use this:
n = Math.round((n - subtrahend) * multiplier) / multiplier;
instead of the following lines using `rounded`
*/
const rounded = Math.round((n - subtrahend) * multiplier) / multiplier;
if (verbose) {
log("detail", `Rounded ${n} to ${rounded}`);
}
n = rounded;
}
return n;
}
// ===== Testing
const cbVerbose = document.querySelector("input[type=checkbox]");
const btnRun = document.querySelector("input[type=button]");
const output = document.querySelector(".output");
const errors = document.querySelector(".errors");
function log(cls, msg) {
/*
output.insertAdjacentText("beforeend", "\r\n" + msgs.join(" "));
*/
const div = document.createElement("div");
div.className = cls;
div.textContent = msg;
output.appendChild(div);
}
let verbose = cbVerbose.checked;
function test(n, expected) {
const rounded = roundTiesDown(n, 2);
const good = rounded === expected;
log(
good ? "good" : "error",
`${n} => ${rounded} ${good ? "OK" : `<== ERROR, expected ${expected}`}`
);
return good ? 0 : 1;
}
function runTests() {
verbose = cbVerbose.checked;
output.textContent = "";
const errorcount =
test(5.425, 5.42) +
test(5.555556, 5.56) +
test(12.3456789, 12.35) +
test(1.125, 1.12) +
test(2.336, 2.34) +
test(2, 2) +
test(-5.425, -5.43);
errors.textContent = errorcount === 0 ? "All passed" : `Errors: ${errorcount}`;
errors.className = errorcount === 0 ? "good" : "error";
}
btnRun.addEventListener("click", runTests);
runTests();html {
box-sizing: border-box;
font-family: sans-serif;
}
*, *:before, *:after {
box-sizing: inherit;
}
html, body {
height: 100%;
overflow: hidden;
padding: 0;
margin: 0;
}
body {
padding: 4px;
display: flex;
flex-direction: column;
font-size: 14px;
}
.panel {
order: 1;
border-bottom: 1px solid black;
padding-bottom: 2px;
}
.output {
order: 2;
flex-grow: 1;
white-space: pre;
font-family: monospace;
overflow: auto;
}
.good {
color: #060;
}
.error {
color: #C00;
}
.detail {
color: #aaa;
}<div class="panel">
<label style="user-select: none">
<input type="checkbox">
Verbose output
</label>
<input type="button" value="Run Tests">
<span class="errors"></span>
</div>
<div class="output"></div>Note that last result for the negative number. If you want to round toward zero rather than "down," you change this line:
n = Math.round((n - subtrahend) * multiplier) / multiplier;
to this, which allows for the sign of n:
n = Math.round((n + (n < 0 ? subtrahend : -subtrahend)) * multiplier) / multiplier;
and change the name of the function, since it no longer rounds down (perhaps roundTiesToZero).
Live Example:
// Get a function to convert numbers to string without going to scientific notation
let numberToString;
if (typeof Intl === "object" && typeof Intl.NumberFormat === "function") {
// Intl.NumberFormat lets us do this properly
const format = new Intl.NumberFormat(undefined, {
style: "decimal",
useGrouping: false,
maximumFractionDigits: 20
});
numberToString = n => format.format(n);
} else {
// Fall back to toString on platforms without Intl.NumberFormat
// (all major browsers have it, including IE11 -
// https://caniuse.com/#feat=mdn-javascript_builtins_intl_numberformat)
const rexContainsE = /e/i;
numberToString = n => {
const str = n.toString();
if (rexContainsE.test(str)) {
// Went to scientific notation
throw new Error("Can't handle numbers this big on this platform");
}
return str;
};
}
// Get the currentPlaces number of significant places in the given number
function significantFractionalPlaces(n) {
const str = numberToString(n);
const idx = str.indexOf(".");
return idx === -1 ? 0 : str.length - idx - 1;
}
// Round the given number to the given number of places, but rounding ties down
// (0.5 rounds to 0 instead of 1, 0.55 rounds to 0.5 instead of 0.6, etc.)
function roundTiesToZero(n, places) {
if (places < 1) {
throw new Error(`Received places=${places}, but must be >=1`);
}
let currentPlaces = significantFractionalPlaces(n)
// Round ties down at each level, e.g. (if places = 2):
// 0.55556 => 0.5556
// 0.5556 => 0.556
// 0.556 => 0.56
// and
// 0.55555 => 0.5555 (would be 0.5556 with "normal" rounding)
// 0.5555 => 0.555
// 0.555 => 0.55
while (currentPlaces > places) {
const subtrahend = 1 / Math.pow(10, currentPlaces);
--currentPlaces;
const multiplier = Math.pow(10, currentPlaces);
/* For your real function, use this:
n = Math.round((n + (n < 0 ? subtrahend : -subtrahend)) * multiplier) / multiplier;
instead of the following lines using `rounded`
*/
const rounded = Math.round((n + (n < 0 ? subtrahend : -subtrahend)) * multiplier) / multiplier;
if (verbose) {
log("detail", `Rounded ${n} to ${rounded}`);
}
n = rounded;
}
return n;
}
// ===== Testing
const cbVerbose = document.querySelector("input[type=checkbox]");
const btnRun = document.querySelector("input[type=button]");
const output = document.querySelector(".output");
const errors = document.querySelector(".errors");
function log(cls, msg) {
/*
output.insertAdjacentText("beforeend", "\r\n" + msgs.join(" "));
*/
const div = document.createElement("div");
div.className = cls;
div.textContent = msg;
output.appendChild(div);
}
let verbose = cbVerbose.checked;
function test(n, expected) {
const rounded = roundTiesToZero(n, 2);
const good = rounded === expected;
log(
good ? "good" : "error",
`${n} => ${rounded} ${good ? "OK" : `<== ERROR, expected ${expected}`}`
);
return good ? 0 : 1;
}
function runTests() {
verbose = cbVerbose.checked;
output.textContent = "";
const errorcount =
test(5.425, 5.42) +
test(5.555556, 5.56) +
test(12.3456789, 12.35) +
test(1.125, 1.12) +
test(2.336, 2.34) +
test(2, 2) +
test(-5.425, -5.42);
errors.textContent = errorcount === 0 ? "All passed" : `Errors: ${errorcount}`;
errors.className = errorcount === 0 ? "good" : "error";
}
btnRun.addEventListener("click", runTests);
runTests();html {
box-sizing: border-box;
font-family: sans-serif;
}
*, *:before, *:after {
box-sizing: inherit;
}
html, body {
height: 100%;
overflow: hidden;
padding: 0;
margin: 0;
}
body {
padding: 4px;
display: flex;
flex-direction: column;
font-size: 14px;
}
.panel {
order: 1;
border-bottom: 1px solid black;
padding-bottom: 2px;
}
.output {
order: 2;
flex-grow: 1;
white-space: pre;
font-family: monospace;
overflow: auto;
}
.good {
color: #080;
}
.error {
color: #C00;
}
.detail {
color: #aaa;
}<div class="panel">
<label style="user-select: none">
<input type="checkbox">
Verbose output
</label>
<input type="button" value="Run Tests">
<span class="errors"></span>
</div>
<div class="output"></div>