Grab word and character counts in string

StackOverflow https://stackoverflow.com/questions/15028652

Question

I'm trying to write a super-efficient method that operates in two "modes" (WORD and CHARACTER) that accepts a String and tells me the number of words (separated by 1+ whitespaces) or characters (non-whitespace characters) in it:

public int getCount(String toExamine, boolean wordMode) {
    int count = 0;

    if(wordMode) {
        // Return the number of words.
    }
    else {
        // Return the number of characers.
    }

    return count;
}

I know I could accomplish the WORD mode version using a StringTokenizer:

StringTokenizer tokenizer = new StringTokenizer(" ");

But I have absolutely no clue as to what to use for the CHARACTER mode (the number of non-whitespace characters). I'm sure I could use something crude like:

for(int i = 0; i < toExamine.length; i++)
    if(Character.isSpace(toExamine.charAt(i)))
        count++;

But that is sort of ugly and might not be the most efficient way of doing this (same for the StringTokenizer piece). Could a regex be used here, or some other Java String/Character madness that would get me what I need in super-efficient fashion? I'm working on tens of millions of String here. Thanks in advance.

Was it helpful?

Solution

covert to char array and and iterate with for loop

int charCount =0;
for(int i=0; i<sentence.length(); i++) {
    if(!Character.isWhitespace(sentence.charAt(i))) {
        charCount++;
    }
}

In other way replace all whitespace and count the length with below code

int charcount = 0;
String newSentence =sentence.replaceAll("\\s+", "");
charcount = newSentence.length();

OTHER TIPS

This is not faster then the for loop, but if you need to use regular expressions you can try something like:

int noSpaces=toExamine.split("\\s+").length-1;

The number pf characters will be:

int noChar=toExamine.length-noSpaces;

The test program below produces the following result. The program will output 5 sets of such result, but I only show one here. The lines with // are my annotation, not the output of the program.

// Percentage of non-space over space is approximately 0.857
// Length of the full string generated is 1 075 662
0.857 1075662
// Name_of_method (Result): 15_Runs_In_Microseconds | Average_In_Microseconds
countWords_1 (131489): 20465 20240 21045 20193 20000 19972 20551 39489 19859 19971 19889 19877 20049 19900 19949 | 21429
countWords_2 (131489): 255500 258723 254543 255956 253606 263549 254096 254402 254191 254296 253752 261501 260788 261574 254178 | 256710
countWords_3 (131489): 26225 25022 24830 24829 24545 24819 25459 24625 25628 24700 24936 24794 24794 24849 25026 | 25005
countWords_4 (131489): 24537 24169 25283 24862 23863 23902 24068 23906 51472 23731 23889 23844 23832 24275 23896 | 25968
countWords_5 (131489): 81087 112095 80008 81290 81472 80581 80717 80460 79870 80557 80694 80923 145686 80564 80849 | 87123
countWords_6 (131489): 114391 114146 111946 111873 112331 167207 134117 118217 112843 112804 113533 111834 112830 112392 118181 | 118576
countChars_1 (922546): 150507 109102 150453 111352 149753 108099 153842 109034 150817 117258 149219 108194 152839 110340 149524 | 132022
countChars_2 (922546): 28779 29473 52499 27182 26519 27743 26717 27161 26451 27060 26307 27309 26350 62824 33134 | 31700
countChars_3 (922546): 25408 25127 24980 24832 24624 24671 24848 24712 24634 24622 24607 24613 24661 24765 24883 | 24799
countChars_4 (922546): 81489 82246 80906 80718 80803 81147 81113 81798 81030 81024 108508 80768 80780 80671 80753 | 82916
countChars_5 (922546): 26086 25546 24846 43734 25016 25083 24894 25530 25031 25041 25114 24935 25358 24895 43498 | 27640
countChars_6 (922546): 102559 102257 101381 101589 103432 101739 102794 129472 101305 101834 103124 101486 101254 102874 101481 | 103905

countWords_2 and countWords_6 are one-liner methods involving tricks with regex and replaceAll, which is very slow compared to other methods. countWords_5 uses a pre-compiled Pattern to do matching, faster than the one-liners with replaceAll, but is still slower compare to others.

countWords_3 and countWords_4 are simple looping, but with some minor difference. The timing doesn't show a conclusive difference. (I look for consistency in whether the timing is bigger or smaller, and the difference in timing should be at least around 5 ms).

countWords_1 uses StringTokenizer with the default delimiters, which doesn't include Unicode characters. Therefore, it doesn't make a good comparison here, since the semantic is completely different.

For counting number of words (defined as a sequence of non-whitespace characters), simple looping is faster than the regex methods that I can think of.

countChars_1 and countChars_6 are one-liner solutions involving tricks with regex and replaceAll. Again, it is slower than countChars_4, which uses pre-compiled Pattern. And again, all regex solutions are slower than simple looping.

countChars_2, countChars_3 and countChars_5 are some variations of simple looping. The difference in countChars_3 and countChars_5 from many runs I have observed is not very consistent and therefore non-conclusive. But countChars2 is usually slightly slower, possibly due to new memory has to be allocated to the char[] returned by toCharArray function.

I don't guarantee that the methods I have here are the fastest, but it shows some idea about how simple looping compares to regex solutions.

You can run this test program and decide for yourself. I have written the test so that you can freely:

  • Change the length of the generated test string and how frequent space characters appears.

    Currently, the length of the test string is random between 700 000 to 1 300 000 characters, and the non-space to space character ratio varies between 4:1 to 9:1 (I take a guess for general text). You can set the FLUCTUATION to 0, so that the length or the ratio is fixed - very useful when you want to test edge cases.

  • Replace how the test string is generated (real data instead of randomly generated string).

    Currently, a subset of ASCII characters is used: some 64 non-space characters; space, new line, tab and carriage return are used as whitespace characters. There are Unicode whitespace characters, but not included in the current test.

  • Add new method to test, marked with @Test annotation.
import java.util.regex.Pattern;
import java.util.regex.Matcher;

import java.util.Arrays;
import java.util.ArrayList;
import java.util.Random;
import java.util.StringTokenizer;

import java.lang.reflect.Method;

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.lang.annotation.ElementType;

class TestStringProcessing_15028652 {

  @Retention(RetentionPolicy.RUNTIME)
  @Target(ElementType.METHOD)
  private @interface Test {};

  // From 0.80 - 0.90 (4:1 to 9:1 non-space:space characters ratio)
  private static final double NON_SPACE_RATIO = 0.85;
  private static final double NON_SPACE_RATIO_FLUCTUATION = 0.05;

  // With the way the test is written, it is not going to work well with small input (1000 is NOT enough)
  // Currently set to 700 000 - 1 300 000 characters
  private static final int NUM_CHARS = 1000000;
  private static final int NUM_CHARS_FLUCTUATION = 300000;

  // Some whitespace characters
  private static final char WHITESPACES[] = {' ', '\t', '\r', '\n'};

  // Number of times to run all methods
  private static final int NUM_OUTER = 5;
  // Number of times to run each method
  private static final int NUM_REPEAT = 15;

  static {
    for (int i = 0; i < WHITESPACES.length; i++) {
      assert(Character.isWhitespace(WHITESPACES[i]));
    }
  }

  private static Random random = new Random();

  private static String generateInput() {

    double nonSpaceRatio = NON_SPACE_RATIO + random.nextDouble() * 2 * NON_SPACE_RATIO_FLUCTUATION - NON_SPACE_RATIO_FLUCTUATION;
    int numChars = NUM_CHARS + random.nextInt(2 * NUM_CHARS_FLUCTUATION) - NUM_CHARS_FLUCTUATION;

    System.out.printf("%.3f %d\n", nonSpaceRatio, numChars);

    StringBuffer output = new StringBuffer();

    for (int i = 0; i < numChars; i++) {
      if (random.nextDouble() < nonSpaceRatio) {
        output.append((char) (random.nextInt(64) + '0'));
      } else {
        output.append(WHITESPACES[random.nextInt(WHITESPACES.length)]);
      }
    }

    return output.toString();
  }

  private static ArrayList<Method> getTestMethods() {
    Class<?> klass = null;
    try {
      klass = Class.forName(Thread.currentThread().getStackTrace()[1].getClassName());
    } catch (Exception e) {
      e.printStackTrace();
      System.err.println("Something really bad happened. Bailling out...");
      System.exit(1);
    }
    Method[] methods = klass.getMethods();
    // System.out.println(klass);
    // System.out.println(Arrays.toString(methods));

    ArrayList<Method> testMethods = new ArrayList<Method>();

    for (Method method: methods) {
        if (method.isAnnotationPresent(Test.class)) {
          testMethods.add(method);
        }
    }

    return testMethods;
  }


  public static void runTestReflection() {
    ArrayList<Method> methods = getTestMethods();

    for (int t = 0; t < NUM_OUTER; t++) {
      String input = generateInput();

      for (Method method: methods) {

        try {
          System.out.print(method.getName() + " (" + method.invoke(null, input) + "): ");
        } catch (Exception e) {
          e.printStackTrace();
        }

        long sum = 0;
        for (int i = 0; i < NUM_REPEAT; i++) {
          long start, end;
          Object result;

          try {
            start = System.nanoTime();
            result = method.invoke(null, input);
            end = System.nanoTime();

            System.out.print((end - start) / 1000 + " ");
            sum += (end - start) / 1000;
          } catch (Exception e) {
            e.printStackTrace();
          }
        }

        System.out.println("| " + sum / NUM_REPEAT);
      }

      System.out.println();
    }
  }

  public static void main(String args[]) {
    runTestReflection();
  }

  @Test
  public static int countWords_1(String input) {
    // WARNING: This is NOT the same as isWhitespace, since isWhitespace
    // also consider Unicode characters.
    return new StringTokenizer(input).countTokens();
  }

  @Test
  public static int countWords_2(String input) {
    return input.replaceAll("\\S+", "$0 ").length() - input.length();
  }

  @Test
  public static int countWords_3(String input) {
    int count = 0;
    boolean in = false;

    for (int i = 0; i < input.length(); i++) {
      if (!Character.isWhitespace(input.charAt(i))) {
        if (!in) {
          in = true;
          count++;
        }
      } else {
        in = false;
      }
    }

    return count;
  }

  @Test
  public static int countWords_4(String input) {
    int count = 0;

    for (int i = 0; i < input.length(); i++) {
      if (!Character.isWhitespace(input.charAt(i))) {
        do {
          i++;
        } while (i < input.length() && !Character.isWhitespace(input.charAt(i)));
        count++;
      }
    }

    return count;
  }

  @Test
  public static int countWords_5(String input) {
    int count = 0;
    Matcher m = p.matcher(input);

    while (m.find()) {
      count++;
    }

    return count;
  }

  @Test
  public static int countWords_6(String input) {
    return input.replaceAll("\\s*+\\S++\\s*+", " ").length();
  }

  @Test
  public static int countChars_1(String input) {
    return input.replaceAll("\\s+", "").length();
  }

  @Test
  public static int countChars_2(String input) {
    int count = 0;
    for (char c: input.toCharArray()) {
      if (!Character.isWhitespace(c)) {
        count++;
      }
    }

    return count;
  }

  @Test
  public static int countChars_3(String input) {
    int count = 0;
    for (int i = 0; i < input.length(); i++) {
      if (!Character.isWhitespace(input.charAt(i))) {
        count++;
      }
    }

    return count;
  }

  private static Pattern p = Pattern.compile("\\S+");

  @Test
  public static int countChars_4(String input) {
    Matcher m = p.matcher(input);
    int count = 0;

    while (m.find()) {
      count += m.end() - m.start();
    }

    return count;
  }

  @Test
  public static int countChars_5(String input) {
    int count = input.length();
    for (int i = 0; i < input.length(); i++) {
      if (Character.isWhitespace(input.charAt(i))) {
        count--;
      }
    }

    return count;
  }

  @Test
  public static int countChars_6(String input) {
    return input.length() - input.replaceAll("\\S+", "").length();
  }
}
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