What is the correct regex to search for a specific pattern in these strings?

So I have one big file containing a bunch of weather data. I have to highlight each line from a large file into a corresponding state file. This will create a total of 50 new state files with their own data.

The large file contains about 1 million lines of entries like this:

COOP:166657,'NEW IBERIA AIRPORT ACADIANA REGIONAL LA US',200001,177,553

      

Although the name of the station can change and have a different number of words.

This is the regex I'm using:

Pattern p = Pattern.compile(".* ([A-Z][A-Z]) US.*"); 
Matcher m = p.matcher(line);

      

When I run my program, there are still instances of strings where the pattern cannot be found.

This is my program:

package climate;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Arrays;
import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * This program will read in a large file containing many stations and states,
 * and output in order the stations to their corresponding state file.
 * 
 * Note: This take a long time depending on processor. It also appends data to
 * the files so you must remove all the state files in the current directory
 * before running for accuracy.
 * 
 * @author Marcus
 *
 */

public class ClimateCleanStates {

    public static void main(String[] args) throws IOException {

        Scanner in = new Scanner(System.in);
        System.out
                .println("Note: This program can take a long time depending on processor.");
        System.out
                .println("It is also not necessary to run as state files are in this directory.");
        System.out
                .println("But if you would like to see how it works, you may continue.");
        System.out.println("Please remove state files before running.");
        System.out.println("\nIs the States directory empty?");
        String answer = in.nextLine();

        if (answer.equals("N")) {
            System.exit(0);
            in.close();
        }
        System.out.println("Would you like to run the program?");
        String answer2 = in.nextLine();
        if (answer2.equals("N")) {
            System.exit(0);
            in.close();
        }

        String[] statesSpaced = new String[51];

        File statefile, dir, infile;

        // Create files for each states
        dir = new File("States");
        dir.mkdir();


        infile = new File("climatedata.csv");
        FileReader fr = new FileReader(infile);
        BufferedReader br = new BufferedReader(fr);

        String line;
        System.out.println();

        // Read in climatedata.csv
        // Probably need to implement ClimateRecord class
        final long start = System.currentTimeMillis();
        while ((line = br.readLine()) != null) {
            // Remove instances of -9999

            if (!line.contains("-9999")) {



                        Pattern p = Pattern.compile("^.* ([A-Z][A-Z]) US.*$"); 
                        Matcher m = p.matcher(line);
                        String stateFileName = null;

                        if(m.find()){
                            //System.out.println(m.group(1));
                            stateFileName = m.group(1);
                        } else {
                            System.out.println("Could not find abbreviation");
                        }

                        /*
                        stateFileName = "States/" + stateFileName + ".csv";
                        statefile = new File(stateFileName);

                        FileWriter stateWriter = new FileWriter(statefile, true);
                        stateWriter.write(line + "\n");
                        // Progress reporting
                        System.out.printf("Writing [%s] to file [%s]\n", line,
                                statefile);
                        stateWriter.flush();
                        stateWriter.close();
                        */





            }
        }
        System.out.println("Elapsed " + (System.currentTimeMillis() - start) + " ms");
        br.close();
        fr.close();
        in.close();

    }

}

      

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5 answers


I think you need to look around functions, they assert that something must precede or follow an expression that you match, but are not included in the result.

(?<= )[A-Z][A-Z](?= US)

      

(?<= )

must be a space before



[A-Z][A-Z]

exactly two uppercase letters

(?= US)

must be a space and US letters after

Maybe it will be more stable with the look: (? = US) maybe (? = US ',) for example.

+1


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Depends on what you want to extract exaccty, but if you use a pattern like



Pattern.compile("(.*):(.*),'(.*)',(.*),(.*),(.*)");
Matcher m = p.matcher(line);
if(m.find()) {
  // here you can use with i from 1 to 6
  m.group(i); 

  //and access the 6 tokens:
  //COOP
  //166657
  //NEW IBERIA AIRPORT ACADIANA REGIONAL LA US
  //200001
  //177
  //553
}

      

+1


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Instead

".* ([A-Z][A-Z]) US.*"

If some states are not abbreviated, try:

" ([a-z][A-Z])+ US'"

0


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Pay special attention to the beginning of the ^

line, not greedy group (.*?)

, end of the line $

, DOTALL

and MULTILINE

.

Pattern regex = Pattern.compile("^(.*?):(.*?),'(.*?)',(.*?),(.*?),(.*?)$", Pattern.DOTALL | Pattern.MULTILINE);

      


Regex DEMO:

https://regex101.com/r/bX0rS3/1


Live JAVA example:

http://ideone.com/uAUaJT


Regex Explanation:

^(.*?):(.*?),'(.*?)',(.*?),(.*?),(.*?)$

Options: Case sensitive; Exact spacing; Dot matches line breaks; ^$ match at line breaks; Default line breaks

Assert position at the beginning of a line (at beginning of the string or after a line break character) (carriage return and line feed, next line, line separator, paragraph separator) «^»
Match the regex below and capture its match into backreference number 1 «(.*?)»
   Match any single character «.*?»
      Between zero and unlimited times, as few times as possible, expanding as needed (lazy) «*?»
Match the character ":" literally «:»
Match the regex below and capture its match into backreference number 2 «(.*?)»
   Match any single character «.*?»
      Between zero and unlimited times, as few times as possible, expanding as needed (lazy) «*?»
Match the character string ",'" literally «,'»
Match the regex below and capture its match into backreference number 3 «(.*?)»
   Match any single character «.*?»
      Between zero and unlimited times, as few times as possible, expanding as needed (lazy) «*?»
Match the character string "'," literally «',»
Match the regex below and capture its match into backreference number 4 «(.*?)»
   Match any single character «.*?»
      Between zero and unlimited times, as few times as possible, expanding as needed (lazy) «*?»
Match the character "," literally «,»
Match the regex below and capture its match into backreference number 5 «(.*?)»
   Match any single character «.*?»
      Between zero and unlimited times, as few times as possible, expanding as needed (lazy) «*?»
Match the character "," literally «,»
Match the regex below and capture its match into backreference number 6 «(.*?)»
   Match any single character «.*?»
      Between zero and unlimited times, as few times as possible, expanding as needed (lazy) «*?»
Assert position at the end of a line (at the end of the string or before a line break character) (carriage return and line feed, next line, line separator, paragraph separator) «$»

      

0


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You can confirm that this is the abbreviation of the US state:

\s(?:(A[KLRZ]|C[AOT]|D[CE]|FL|GA|HI|I[ADLN]|K[SY]|LA|M[ADEINOST]|N[CDEHJMVY]|O[HKR]|P[AR]|RI|S[CD]|T[NX]|UT|V[AIT]|W[AIVY])(?:\sUS'|'))

      

Demo

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