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Java separation with math expression

I am trying to break down a mathematical expression.

String number = "100+500";

String[] split = new String[3];

I want to do

  • split [0] = "100"
  • split [1] = "+"
  • split [2] = "500"

I tried this, but I do not know what to write for separation.

split = number.split(????);
+4
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5 answers

You want to split between numbers and numbers without using any input ... you need to look around:

String[] split = number.split("(?<=\\d)(?=\\D)|(?<=\\D)(?=\\d)");

What the hell is a regular train wreck?

He expresses the initial sentence of this answer:

  • (?<=\d) means the previous character is a digit
  • (?=\D) means the next character is not a digit
  • (?<=\d)(?=\D) together will match between digit and digit
  • regexA|regexB , , , , , .

, , - .

:

String number = "100+500-123/456*789";
String[] split = number.split("(?<=\\d)(?=\\D)|(?<=\\D)(?=\\d)");
System.out.println(Arrays.toString(split));

:

[100, +, 500, -, 123, /, 456, *, 789]
+6

, . :

/**
 * Splits the given {@link String} at the operators +, -, * and /
 * 
 * @param string
 *            the {@link String} to be split.
 * @throws NullPointerException
 *             when the given {@link String} is null.
 * @return a {@link List} containing the split string and the operators.
 */
public List<String> split(String string) throws NullPointerException {
    if (string == null)
        throw new NullPointerException("the given string is null!");
    List<String> result = new ArrayList<String>();

    // operators to split upon
    String[] operators = new String[] { "+", "-", "*", "/" };

    int index = 0;
    while (index < string.length()) {
        // find the index of the nearest operator
        int minimum = string.length();
        for (String operator : operators) {
            int i = string.indexOf(operator, index);
            if (i > -1)
                minimum = Math.min(minimum, i);
        }

        // if an operator is found, split the string
        if (minimum < string.length()) {
            result.add(string.substring(index, minimum));
            result.add("" + string.charAt(minimum));
            index = minimum + 1;
        } else {
            result.add(string.substring(index));
            break;
        }
    }

    return result;
}

:

System.out.println(split("100+10*6+3"));
System.out.println(split("100+"));

:

[100, +, 10, *, 6, +, 3]
[100, +]
+3

Pattern/Matcher Java:

    String expression = "100+34";
    Pattern p = Pattern.compile("(\\d+)|(\\+)");
    Matcher m = p.matcher(expression);
    String[] elems = new String[m.groupCount() +1];
    int i=0;

    while(m.find())
    {
        elems[i++] = m.group();
    }
+2

- , ; pad + :

String number = "100+500";
number = number.replace("+", " + ");

:

String[] split = number.split(" ");

:

split[0] = "100";
split[1] = "+";
split[2] = "500";

, , :

public static String replacing(String s) {
   String[] chars = {"+", "-", "/", "="};

   for (String character : chars) {
      if (s.contains(character)) {
         s = s.replace(character, " " + character + " ");//not exactly elegant, but it works
      }
   }
   return s;
}

//in main method
number = replacing(number);
String[] split = number.split(" ");
+1

, . mXparser , . , :

"100 + 500":

import org.mariuszgromada.math.mxparser.*;
...
...
Expression e = new Expression("100+500");
mXparser.consolePrintTokens( e.getCopyOfInitialTokens() );

:

[mXparser-v.4.0.0]  --------------------
[mXparser-v.4.0.0] | Expression tokens: |
[mXparser-v.4.0.0]  ---------------------------------------------------------------------------------------------------------------
[mXparser-v.4.0.0] |    TokenIdx |       Token |        KeyW |     TokenId | TokenTypeId |  TokenLevel |  TokenValue |   LooksLike |
[mXparser-v.4.0.0]  ---------------------------------------------------------------------------------------------------------------
[mXparser-v.4.0.0] |           0 |         100 |       _num_ |           1 |           0 |           0 |       100.0 |             |
[mXparser-v.4.0.0] |           1 |           + |           + |           1 |           1 |           0 |         NaN |             |
[mXparser-v.4.0.0] |           2 |         500 |       _num_ |           1 |           0 |           0 |       500.0 |             |
[mXparser-v.4.0.0]  ---------------------------------------------------------------------------------------------------------------

"2 * sin (x) + (3/cos (y) -e ^ (sin (x) + y)) + 10":

import org.mariuszgromada.math.mxparser.*;
...
...
Argument x = new Argument("x");
Argument y = new Argument("y");
Expression e = new Expression("2*sin(x)+(3/cos(y)-e^(sin(x)+y))+10", x, y);
mXparser.consolePrintTokens( e.getCopyOfInitialTokens() );

:

[mXparser-v.4.0.0]  --------------------
[mXparser-v.4.0.0] | Expression tokens: |
[mXparser-v.4.0.0]  ---------------------------------------------------------------------------------------------------------------
[mXparser-v.4.0.0] |    TokenIdx |       Token |        KeyW |     TokenId | TokenTypeId |  TokenLevel |  TokenValue |   LooksLike |
[mXparser-v.4.0.0]  ---------------------------------------------------------------------------------------------------------------
[mXparser-v.4.0.0] |           0 |           2 |       _num_ |           1 |           0 |           0 |         2.0 |             |
[mXparser-v.4.0.0] |           1 |           * |           * |           3 |           1 |           0 |         NaN |             |
[mXparser-v.4.0.0] |           2 |         sin |         sin |           1 |           4 |           1 |         NaN |             |
[mXparser-v.4.0.0] |           3 |           ( |           ( |           1 |          20 |           2 |         NaN |             |
[mXparser-v.4.0.0] |           4 |           x |           x |           0 |         101 |           2 |         NaN |             |
[mXparser-v.4.0.0] |           5 |           ) |           ) |           2 |          20 |           2 |         NaN |             |
[mXparser-v.4.0.0] |           6 |           + |           + |           1 |           1 |           0 |         NaN |             |
[mXparser-v.4.0.0] |           7 |           ( |           ( |           1 |          20 |           1 |         NaN |             |
[mXparser-v.4.0.0] |           8 |           3 |       _num_ |           1 |           0 |           1 |         3.0 |             |
[mXparser-v.4.0.0] |           9 |           / |           / |           4 |           1 |           1 |         NaN |             |
[mXparser-v.4.0.0] |          10 |         cos |         cos |           2 |           4 |           2 |         NaN |             |
[mXparser-v.4.0.0] |          11 |           ( |           ( |           1 |          20 |           3 |         NaN |             |
[mXparser-v.4.0.0] |          12 |           y |           y |           1 |         101 |           3 |         NaN |             |
[mXparser-v.4.0.0] |          13 |           ) |           ) |           2 |          20 |           3 |         NaN |             |
[mXparser-v.4.0.0] |          14 |           - |           - |           2 |           1 |           1 |         NaN |             |
[mXparser-v.4.0.0] |          15 |           e |           e |           2 |           9 |           1 |         NaN |             |
[mXparser-v.4.0.0] |          16 |           ^ |           ^ |           5 |           1 |           1 |         NaN |             |
[mXparser-v.4.0.0] |          17 |           ( |           ( |           1 |          20 |           2 |         NaN |             |
[mXparser-v.4.0.0] |          18 |         sin |         sin |           1 |           4 |           3 |         NaN |             |
[mXparser-v.4.0.0] |          19 |           ( |           ( |           1 |          20 |           4 |         NaN |             |
[mXparser-v.4.0.0] |          20 |           x |           x |           0 |         101 |           4 |         NaN |             |
[mXparser-v.4.0.0] |          21 |           ) |           ) |           2 |          20 |           4 |         NaN |             |
[mXparser-v.4.0.0] |          22 |           + |           + |           1 |           1 |           2 |         NaN |             |
[mXparser-v.4.0.0] |          23 |           y |           y |           1 |         101 |           2 |         NaN |             |
[mXparser-v.4.0.0] |          24 |           ) |           ) |           2 |          20 |           2 |         NaN |             |
[mXparser-v.4.0.0] |          25 |           ) |           ) |           2 |          20 |           1 |         NaN |             |
[mXparser-v.4.0.0] |          26 |           + |           + |           1 |           1 |           0 |         NaN |             |
[mXparser-v.4.0.0] |          27 |          10 |       _num_ |           1 |           0 |           0 |        10.0 |             |
[mXparser-v.4.0.0]  ---------------------------------------------------------------------------------------------------------------

To understand what Token.tokenId and Token.tokenTypeId mean, you need to refer to the API documentation and the parsertokens section. For example, in the Operator class you have

  • Operator.TYPE_ID - this corresponds to Token.tokenTypeId if the token is recognized as an operator
  • Operator.OPERATOR_NAME_ID - this corresponds to Token.tokenId if the token is recognized as defined by OPERATOR_NAME.

Please follow the mXparser tutorial for a better understanding.

Regards

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Source: https://habr.com/ru/post/1570220/

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