valueToString function

String valueToString(double value, int significantFigures, bool removeTrailingZeros, bool useScientificNotation,)

Given a double value it returns its representation as a string with few tweaks: significantFigures is the number of significant figures to keep, removeTrailingZeros say if non important zeros should be removed. E.g. 1.000000 --> 1

Implementation

String valueToString(
  double value,
  int significantFigures,
  bool removeTrailingZeros,
  bool useScientificNotation,
) {
  //Round to a fixed number of significant figures
  String stringValue;
  if (useScientificNotation) {
    stringValue = value.toStringAsPrecision(significantFigures);
  } else {
    stringValue = value.toStringAsFixed(significantFigures);
  }

  /**
   * [stringValue] can be in multiple form:
   *  - x     (an integer)
   *  - x.y   (a decimal)
   *  - xez   (integer with an exponential part)
   *  - x.yez (decimal with an exponential part)
   */

  List<String> splittedNumbers = stringValue.split('.');
  String integerPart = splittedNumbers[0];
  String? decimalPart, exponentialPart;

  // x.y and x.yez
  if (splittedNumbers.length == 2) {
    splittedNumbers = splittedNumbers[1].split('e');
    decimalPart = splittedNumbers[0];

    // x.yez
    if (splittedNumbers.length == 2) {
      exponentialPart = splittedNumbers[1];
    }
  }
  // x and xez
  else {
    splittedNumbers = splittedNumbers[0].split('e');

    // xez
    if (splittedNumbers.length == 2) {
      integerPart = splittedNumbers[0];
      exponentialPart = splittedNumbers[1];
    }
  }

  //if the user want to remove the trailing zeros
  if (removeTrailingZeros && decimalPart != null) {
    //remove trailing zeros (just fractional part)
    int firstZeroIndex = decimalPart.length;
    for (; firstZeroIndex > 0; firstZeroIndex--) {
      String charAtIndex =
          decimalPart.substring(firstZeroIndex - 1, firstZeroIndex);
      if (charAtIndex != '0') break;
    }
    decimalPart = decimalPart.substring(0, firstZeroIndex);
    if (decimalPart == "") {
      decimalPart = null;
    }
  }

  if (!useScientificNotation && exponentialPart != null) {
    // It means that the absolute value of [value] is greater or equal than 1e21
    // (see the documentation of .toStringAsFixed() method)

    /**
     *  There are 2 cases:
     *  - x.ye+z
     *  - xe+z
     */
    int exponentialNumber = int.parse(exponentialPart);
    // x.ye+z
    if (decimalPart != null) {
      if (decimalPart.length < exponentialNumber) {
        decimalPart = decimalPart +
            ''.padRight(exponentialNumber - decimalPart.length, '0');
      }
      integerPart = integerPart + decimalPart.substring(0, exponentialNumber);
      decimalPart = decimalPart.substring(exponentialNumber);
      if (decimalPart == '') decimalPart = null;
    }
    // xe+z
    else {
      integerPart = integerPart + ''.padRight(exponentialNumber, '0');
    }
    exponentialPart = null;
  }

  //Recompose the string
  String finalString = integerPart;
  if (decimalPart != null) {
    finalString = '$finalString.$decimalPart';
  }
  if (exponentialPart != null) {
    finalString = '${finalString}e$exponentialPart';
  }
  return finalString;
}