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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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.
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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
}
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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("^(.*?):(.*?),'(.*?)',(.*?),(.*?),(.*?)$", Pattern.DOTALL | Pattern.MULTILINE);
Regex DEMO:
https://regex101.com/r/bX0rS3/1
Live JAVA example:
Regex Explanation:
^(.*?):(.*?),'(.*?)',(.*?),(.*?),(.*?)$
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) «$»
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