How to extract numbers from a string and get an ar

Question

I have a String variable (basically an English sentence with an unspecified number of numbers) and I'd like to extract all the numbers into an array of integers. I was wondering whether there was a quick solution with regular expressions?

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I used Sean's solution and changed it slightly:

LinkedList<String> numbers = new LinkedList<String>();

Pattern p = Pattern.compile("\\d+");
Matcher m = p.matcher(line); 
while (m.find()) {
   numbers.add(m.group());
}

Answer 1

Pattern p = Pattern.compile("-?\\d+");
Matcher m = p.matcher("There are more than -2 and less than 12 numbers here");
while (m.find()) {
  System.out.println(m.group());
}

... prints -2 and 12.

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-? matches a leading negative sign -- optionally. \d matches a digit, and we need to write \ as \\ in a Java String though. So, \d+ matches 1 or more digits.

Answer 2

  StringBuffer sBuffer = new StringBuffer();
  Pattern p = Pattern.compile("[0-9]+.[0-9]*|[0-9]*.[0-9]+|[0-9]+");
  Matcher m = p.matcher(str);
  while (m.find()) {
    sBuffer.append(m.group());
  }
  return sBuffer.toString();

This is for extracting numbers retaining the decimal

Answer 3

Using Java 8, you can do:

String str = "There 0 are 1 some -2-34 -numbers 567 here 890 .";
int[] ints = Arrays.stream(str.replaceAll("-", " -").split("[^-\\d]+"))
                 .filter(s -> !s.matches("-?"))
                 .mapToInt(Integer::parseInt).toArray();
System.out.println(Arrays.toString(ints)); // prints [0, 1, -2, -34, 567, 890]

If you don't have negative numbers, you can get rid of the replaceAll (and use !s.isEmpty() in filter), as that's only to properly split something like 2-34 (this can also be handled purely with regex in split, but it's fairly complicated).

Arrays.stream turns our String[] into a Stream<String>.

filter gets rid of the leading and trailing empty strings as well as any - that isn't part of a number.

mapToInt(Integer::parseInt).toArray() calls parseInt on each String to give us an int[].

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Alternatively, Java 9 has a Matcher.results method, which should allow for something like:

Pattern p = Pattern.compile("-?\\d+");
Matcher m = p.matcher("There 0 are 1 some -2-34 -numbers 567 here 890 .");
int[] ints = m.results().map(MatchResults::group).mapToInt(Integer::parseInt).toArray();
System.out.println(Arrays.toString(ints)); // prints [0, 1, -2, -34, 567, 890]

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As it stands, neither of these is a big improvement over just looping over the results with Pattern / Matcher as shown in the other answers, but it should be simpler if you want to follow this up with more complex operations which are significantly simplified with the use of streams.

Answer 4

Pattern p = Pattern.compile("[0-9]+");
Matcher m = p.matcher(myString);
while (m.find()) {
    int n = Integer.parseInt(m.group());
    // append n to list
}
// convert list to array, etc

You can actually replace [0-9] with \d, but that involves double backslash escaping, which makes it harder to read.

Answer 5

What about to use replaceAll java.lang.String method:

    String str = "qwerty-1qwerty-2 455 f0gfg 4";      
    str = str.replaceAll("[^-?0-9]+", " "); 
    System.out.println(Arrays.asList(str.trim().split(" ")));

Output:

[-1, -2, 455, 0, 4]

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Description

[^-?0-9]+

• + Between one and unlimited times, as many times as possible, giving back as needed
• -? One of the characters “-?”
• 0-9 A character in the range between “0” and “9”

Answer 6

Extract all real numbers using this.

public static ArrayList<Double> extractNumbersInOrder(String str){

    str+='a';
    double[] returnArray = new double[]{};

    ArrayList<Double> list = new ArrayList<Double>();
    String singleNum="";
    Boolean numStarted;
    for(char c:str.toCharArray()){

        if(isNumber(c)){
            singleNum+=c;

        } else {
            if(!singleNum.equals("")){  //number ended
                list.add(Double.valueOf(singleNum));
                System.out.println(singleNum);
                singleNum="";
            }
        }
    }

    return list;
}


public static boolean isNumber(char c){
    if(Character.isDigit(c)||c=='-'||c=='+'||c=='.'){
        return true;
    } else {
        return false;
    }
}