Java 8 Stream: Find first element after element

Question

I have this list ["z", "1", "3", "x", "y", "00", "x", "y", "4"] that I need to get the first Integer element after the String 00 in this case 4. I am using Java 8 streams but any other method is welcome. Here is my starter code

myList.stream()
      // Remove any non-Integer characters
      .filter((str) -> !"x".equals(str) && !"y".equals(str) && !"z".equals(str))
      .findFirst()
      .orElse("");

That starts me off by removing all non-Integer Strings but gives me 1. Now what I need is to get 4 which is the first element after 00. What should I add to the filter?

@Lebecca I thought that will make my code neat and tidy :-). Anywhoo, lemmi look for another way — Kihats
– Kihats, Commented Mar 17, 2020 at 8:43
Why not just get indexOf "00" and use stream.skip(index).filter(str->isInteger(str)).findFirst() — beatrice
– beatrice, Commented Mar 17, 2020 at 8:44
you can use dropWhile and continue using filter with Java-9+ as in mylist.stream().dropWhile(s -> !s.equals("00")).filter..., but what matters is the problem statement being specific about getting the integers and that too after a pattern 00. — Naman
– Naman, Commented Mar 17, 2020 at 8:50

Lebecca · Accepted Answer · 2020-03-17 08:47:42Z

4

Got from the comment.

 String result = myList.stream().skip(myList.indexOf("00") + 1)
        .filter((str) -> !"x".equals(str) && !"y".equals(str) && !"z".equals(str))
        .findFirst()
        .orElse("");

answered Mar 17, 2020 at 8:47

Lebecca

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4 Comments

Naman Over a year ago

somwhat like the dropWhile suggestion I was making

Kihats Over a year ago

This one worked. Thanks. Didn't think of the skip() method.

Holger Over a year ago

Since this is relying on the List API anyway, myList.subList(myList.indexOf("00") + 1, myList.size()) .stream() would be more efficient.

Lebecca Over a year ago

@Holger My initial intention came same with you. but using stream the whole process is kind of more neat and tidy as Kihats said as requirement in comments.

Gtomika · Accepted Answer · 2020-03-17 08:47:05Z

3

A simple for loop, perhaps. A lot more readable then a stream expression, also more general, since strings like 'x' and 'y' are not hard coded into it.

boolean found00 = false;
int intAfter00 = -1;
for(String str: myList) {
    if("00".equals(str)) {
       found00 = true; //from this point we look for an integer
       continue;
    }
    if(found00) { //looking for an integer
       try {
           intAfter00 = Integer.parseInt(str);
       } catch(Exception e) {
          continue; //this was not an integer
       }
       break;
    }
}
//If intAfter00 is still -1 here then we did not found an integer after 00

answered Mar 17, 2020 at 8:47

Gtomika

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Comments

Santosh Sagar · Accepted Answer · 2020-03-17 08:56:29Z

2

You can try below code.

import java.util.Arrays;
import java.util.List;
import java.util.Optional;

public class Main {

    public static void main(String[] args) {

        List<String> list = Arrays.asList("z", "1", "3", "x", "y", "00", "x", "y", "4");

        String str = "00";

        Optional<String> dataOptional = list.stream().skip(list.indexOf(str)+1).filter(s -> {
            try {
                Integer.parseInt(s);
                return true;
            } catch (NumberFormatException n) {
                return false;
            }
        }).findFirst();

        if (dataOptional.isPresent()) {
            System.out.println("Data is :: " + dataOptional.get());
        } else {
            System.out.println("No integer present after given string");
        }

    }
}

Make sure str is present in list otherwise it will return first integer from the list.

answered Mar 17, 2020 at 8:56

Santosh Sagar

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2 Comments

Kihats Over a year ago

Actually, that's how I want it to work. If it can't find 00 then should return the first integer in the list

Santosh Sagar Over a year ago

Great then.. You can use given code for your purpose.

beatrice · Accepted Answer · 2020-03-17 08:52:21Z

0

int index = myList.indexOf("00");
String result =myList.stream.skip(index).filter(str->isInteger(str)).findFirst().orElse(null);

private boolean isInteger(String str){
 try{
   Integer.parseInt(str);
   return true;
 } catch (NumberFormatException e) {
   return false;
 }
 }

answered Mar 17, 2020 at 8:52

beatrice

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Comments

Ismail · Accepted Answer · 2020-03-17 09:00:52Z

0

You can do as follows using streams:

String result=myList.subList(myList.indexOf("00")+1, myList.size()).stream().filter(string->string.matches("\\d+")).findFirst().get();

This solution gives you a good result even if you are using strings rather than x, y, z.

answered Mar 17, 2020 at 9:00

Ismail

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Comments

Raul Lopes · Accepted Answer · 2020-03-17 09:10:21Z

0

If you don't have the index of list at this moment. You could do something like this

int count = 0;

Stream.of("z", "1", "3", "x", "y", "00", "98", "y", "4")
.peek(element -> {
    if (element.equals("00") || count > 0 && isNumber(element))
        count++;
}).filter(element -> isNumber(element) && count == 3).findFirst().orElse(null);

private boolean isNumber(String element) {
    return element.matches("\\d+");
};

answered Mar 17, 2020 at 9:10

Raul Lopes

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Comments

Subarata Talukder · Accepted Answer · 2021-11-23 05:33:24Z

0

Try it: Suppose you have a list

String[] v = {"z", "1", "3", "x", "y", "00", "x", "y", "4", "5", "y", "7"};

Now find first element after an element:

String result = Stream.of(v).filter(e-> e.matches("^(\\d+)")).dropWhile(e-> !e.contains("00")).skip(1).findFirst().orElse("");
System.out.println(result);

answered Nov 23, 2021 at 5:33

Subarata Talukder

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