RegEx vscode - replace decimal places and round correctly - regex

Question

Is it possible to use regex to round decimal places?
I have lines that look like this but without any spaces (space added for readability).
0, 162.3707542, -162.3707542
128.2, 151.8299471, -23.62994709 // this 151.829 should lead to 151.83
I want to remove all numbers after the second decimal position and if possible round the second decimal position based on the third position.
0, 162.37, -162.37
128.2, 151.82, -23.62 // already working .82
..., 151.83, ... // intended .83 <- this is my question
What is working
The following regex (see this sample on regex101.com) almost does what i want
([0-9]+\.)([0-9]{2})(\d{0,}) // search
$1$2 // replace
My understanding
The search works like this
group: ([0-9]+\.) find 1 up to n numbers and a point
group: ([0-9]{2}) followd by 2 numbers
group: (\d{0,}) followed by 0 or more numbers / digits
In visual-studio-code in the replacement field only group 1 and 2 are referenced $1$2.
This results in this substitution (regex101.com)
Question
Is it possible to change the last digit of $2 (group two) based on the first digit in $3 (group three) ?
My intention is to round correctly. In the sample above this would mean
151.8299471 // source
151.82 // current result
151.83 // desired result 2 was changed to 3 because of third digit 9

Answer 1

It is not only that you need to update the digit of $2. if the number is 199.995 you have to modify all digits of your result.
You can use the extension Regex Text Generator.
You can use a predefined set of regex's.
"regexTextGen.predefined": {
"round numbers": {
"originalTextRegex": "(-?\\d+\\.\\d+)",
"generatorRegex": "{{=N[1]:fixed(2):simplify}}"
}
}
With the same regex (-?\\d+\\.\\d+) in the VSC Find dialog select all number you want, you can use Find in Selection and Alt+Enter.
Then execute the command: Generate text based on Regular Expression.
Select the predefined option and press Enter a few times. You get a preview of the result, you can escape the UI and get back the original text.
In the process you can edit generatorRegex to change the number of decimals or to remove the simplify.

Answer 2

It was easier than I thought, once I found the Number.toFixed(2) method.
Using this extension I wrote, Find and Transform, make this keybinding in your keybindings.json:
{
"key": "alt+r", // whatever keybinding you want
"command": "findInCurrentFile",
"args": {
"find": "(-?[0-9]+\\.\\d{3,})", // only need the whole number as one capture group
"replace": [
"$${", // starting wrapper to indicate a js operation begins
"return $1.toFixed(2);", // $1 from the find regex
"}$$" // ending wrapper to indicate a js operation ends
],
// or simply in one line
// "replace": "$${ return $1.toFixed(2); }$$",
"isRegex": true
},
}
[The empty lines above are there just for readability.]
This could also be put into a setting, see the README, so that a command appears in the Command Palette with the title of your choice.
Also note that javascript rounds -23.62994709 to -23.63. You had -23.62 in your question, I assume -23.63 is correct.
If you do want to truncate things like 4.00 to 4 or 4.20 to 4.2 use this replace instead.
"replace": [
"$${",
"let result = $1.toFixed(2);",
"result = String(result).replace(/0+$/m, '').replace(/\\.$/m, '');",
"return result;",
"}$$"
],

Answer 3

We are able to round-off decimal numbers correctly using regular expressions.
We need basically this regex:
secondDD_regx = /(?<=[\d]*\.[\d]{1})[\d]/g; // roun-off digit
thirdDD_regx = /(?<=[\d]*\.[\d]{2})[\d]/g; // first discard digit
isNonZeroAfterThirdDD_regx = /(?<=[\d]*\.[\d]{3,})[1-9]/g;
isOddSecondDD_regx = /[13579]/g;
Full code (round-off digit up to two decimal places):
const uptoOneDecimalPlaces_regx = /[\+\-\d]*\.[\d]{1}/g;
const secondDD_regx = /(?<=[\d]*\.[\d]{1})[\d]/g;
const thirdDD_regx = /(?<=[\d]*\.[\d]{2})[\d]/g;
const isNonZeroAfterThirdDD_regx = /(?<=[\d]*\.[\d]{3,})[1-9]/g;
const num = '5.285';
const uptoOneDecimalPlaces = num.match(uptoOneDecimalPlaces_regx)?.[0];
const secondDD = num.match(secondDD_regx)?.[0];
const thirdDD = num.match(thirdDD_regx)?.[0];
const isNonZeroAfterThirdDD = num.match(isNonZeroAfterThirdDD_regx)?.[0];
const isOddSecondDD = /[13579]/g.test(secondDD);
// check carry
const carry = !thirdDD ? 0 : thirdDD > 5 ? 1 : thirdDD < 5 ? 0 : isNonZeroAfterThirdDD ? 1 : isOddSecondDD ? 1 : 0;
let roundOffValue;
if(/9/g.test(secondDD) && carry) {
roundOffValue = (Number(`${uptoOneDecimalPlaces}` + `${secondDD ? Number(secondDD) : 0}`) + Number(`0.0${carry}`)).toString();
} else {
roundOffValue = (uptoOneDecimalPlaces + ((secondDD ? Number(secondDD) : 0) + carry)).toString();
}
// Beaufity output : show exactly 2 decimal places if output is x.y or x
const dd = roundOffValue.match(/(?<=[\d]*[\.])[\d]*/g)?.toString().length;
roundOffValue = roundOffValue + (dd=== undefined ? '.00' : dd === 1 ? '0' : '');
console.log(roundOffValue);
For more details check: Round-Off Decimal Number properly using Regular Expression🤔