Doubt with Regex

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Good night.

I need a regular expression that can capture the numbers/expressions before and after a certain character, like this one ^.

For example, in the string below I need her to return me (5 * 77 + 4)^6 and 7^3:

5! + 8 - 5(ln(3)) + (5 * 77 + 4)^6 - 7^3

The expressions I’ve created so far are these:

  • /((\()?(.)+(\))?)+(\^)+((\()?(.)+(\))?)/g

  • /\(*\w+\)*(\^)+\(*\w+\)*/g

It is important that he check if there is only one ^.

In this example there is a functional application of the second case in a string, however I am not able to apply it in javascript.

javascript string regex

  • Try: [ ] This expression uses the denied list.

  • @Denercarvalho, in which case it will not only capture the string excluding the ^?

  • Yes, now I understand what you want, my expression won’t work.

  • You want to isolate only the mathematical operation that uses power ^.

  • That’s right. At this link there is an example that this site works, but when I insert in javascript, it does not return me the correct value.

  • and because the expression cannot recognize the operations that are between relatives, both the right of the power ^ as for the left, only one operation alone 98 22.

  • It does not bring the correct values because groups are missing, see this example: https://regex101.com/r/uL2fQ0/5 But I still can’t get it to pick up other expressions. I’m trying to.

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Well, what I wanted with the capture of these numbers/expressions was to simulate the action of the exponential function with the signal ^.

I got a way to do it, but it wasn’t just with regex.

First, I had to capture everything before the ^ so that syntactically this fit the exponential function. For example:

In the string below, I would capture the (2 - 9), ignoring white spaces, regardless of their quantity:

log(10) + (2 - 9) ^ 5

And then I’d have to do the same with what there was after the ^, what still in the above example would be the 5.

After that I should apply these captures in the javascript function Math, pow() that performs the exponentiation, according to what has already been said, would:

Math.pow((2 - 9), 5)

And finally, I should repeat this capture process>capture>concatenation until there is no more ^ in the midst of string. For so I could have an exponentiation within another exponentiation:

(2 ^ 3)^7

o Javascript

To capture what was before the ^, the code was that:

function captureBefore(string) {
  var result;
  var n = string.indexOf("^");
  var i = n - 1;
  while (!(string.charAt(i) != " ")) {
    --i;
  }
  if (!(/\d/.test(string.charAt(i)))) {
    var nOpen = 1;
    var nClose = 0;
    while (nOpen != nClose) {
      if (string.charAt(i - 1) == ")") {
        ++nOpen;
      } else if (string.charAt(i - 1) == "(") {
        ++nClose;
      }
      i -= 1;
    }
    if (/[a-z]/.test(string.charAt(i - 1))) {
      while ((/[a-zA-Z.]/.test(string.charAt(i - 1)))) {
        i -= 1;
      }
    }
    result = string.substring(i, n);
  } else {
    while (/\d/.test(string.charAt(i)) || /[-|+|.]/.test(string.charAt(i))) {
      i -= 1;
    }
    result = string.substring(i + 1, n);
  }
  return result;
}

And for what was after:

function captureAfter(string) {
  var result;
  var n = string.indexOf("^");
  var i = n + 1;
  while (string.charAt(i) == " " || /[a-zA-Z.]/.test(string.charAt(i))) {
    ++i;
  }
  if (/[-|+]/.test(string.charAt(i))) {
    ++i;
  }
  if (!(/(\d)/.test(string.charAt(i)))) {
    var nOpen = 1;
    var nClose = 0;
    while (nOpen != nClose) {
      if (string.charAt(i + 1) == "(") {
        ++nOpen;
      } else if (string.charAt(i + 1) == ")") {
        ++nClose;
      }
      i += 1;
    }
    result = (string.substring(n + 1, i + 1));
  } else {
    while (/\d/.test(string.charAt(i)) || /[-|+|.]/.test(string.charAt(i))) {
      i += 1;
    }
    result = (string.substring(n + 1, i));
  }
  return result;
}

And for it to repeat itself and function to reach all signals:

if (/\^/g.test(string)) {
  string = string.replace(/\s*\^\s*/g, "^")
  while (/\^/g.test(string)) {
    string = string.replace(captureBefore(string) + "^" + captureAfter(string), "Math.pow(" + captureBefore(string) + ", " + captureAfter(string) + ")");
  }
}

With this I was able to perform the function successfully. But if anyone has an idea that has the same result with less code, I’m still open to possibilities.

Functional example

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