Memo: [Java] Process the read csv (extract, change according to the conditions) and output

background

The workplace collects data on the atmosphere and ultraviolet rays with a Raspberry Pi. If you want to borrow the data and use it as a sample to draw a graph in the project you are doing now, Since weird data was mixed in the middle, I will write down the code that I wrote that it can not be used unless it is formatted.

** Such data **

** Get data every second from 0:00 to 23:59:59 at yyyy / mm / dd hh: mm: ss, atmospheric pressure (hPa), temperature (℃) ** Occasionally, the atmospheric pressure data with 10 at the beginning is mixed.

20180712.csv

2018/07/12 00:00:00,1014.44,28.59
2018/07/12 00:00:01,1014.44,28.59
2018/07/12 00:00:02,1014.46,28.62
2018/07/12 00:00:03,1014.45,28.62
2018/07/12 00:00:04,1014.44,28.59
2018/07/12 00:00:05,1014.45,28.62
2018/07/12 00:00:06,101014.45,28.59
2018/07/12 00:00:07,1014.45,28.62

~ Omitted ~

2018/07/12 23:59:58,1006.29,28.66
2018/07/12 23:59:59,1006.28,28.62

Thing you want to do

** I want to read CSV, perform necessary processing, and output to another name CSV. ** ** -I don't need every second, so I want to write out data every minute. (Extract only 00 seconds per minute) -If the atmospheric pressure data for 00 seconds contains a value such as 101014.45, I would like to change it to 1014.45 and write the data.

** Completed code **

test.java

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class test{

    public static void main(String[] args) {
        process("20180712.csv",  ":00,","output.csv");
    }

    public static void process(String read_file, String searchString, String output_file){

        try(FileReader fr = new FileReader(read_file);BufferedReader br = new BufferedReader(fr);
            FileWriter fw = new FileWriter(output_file);BufferedWriter bw = new BufferedWriter(fw)){

            String line;
            while ((line = br.readLine()) != null) {
                Pattern p = Pattern.compile(searchString);
                Matcher m = p.matcher(line);
                if (m.find()){
                    String[] csvArray;
                    csvArray = line.split(",");
                    String time  = csvArray[0];
                    float press = Float.parseFloat(csvArray[1])%10000;
                    String pressure = String.format("%.2f", press);
                    String temperature  = csvArray[2];
                    String outputLine = String.join(",",time,pressure,temperature);
                    bw.write(outputLine);
                    bw.newLine();
                }else{ 
                }
            }
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }
}

**: pencil: What you are doing **

We are passing three arguments: the file name to be read into the process, the search character, and the output file name. 　　　　process("20180712.csv", ":00,","output.csv");

❶ Search for rows in 0 seconds (": 00,") using Pattern and Matcher ❷ When a row containing 00 seconds is found, split it into an array (csvArray) of String with, (comma). ❸ Atmospheric pressure data (csvArray [1]) is a decimal number, so convert from String type to float type.

• Incidentally, set the remainder after dividing by 10000 as the value. Dividing 101014.45 by 10000 gives the remainder 1014.45 ❹ Convert float type data to String type again
• In addition, round off to the first decimal place and set the value. ❺ Connect the values of each array with (comma) ❻ Output one line and start a new line

Repeat for the number of lines of the file to read from ❶ to ❻

**: pencil: memo **

** Pattern and Matcher used to search **

Matcher can be created by passing a string to the Pattern.matcher () method. The result of the match judgment is returned as true or false.

Pattern pattern = Pattern.compile("U"); //The character string you want to search"U"Create a Pattern to set
Matcher matcher = pattern.matcher("AIUEO"); //Character string to be searched"AIUEO"Create a matcher that searches for

matcher.find()       //Judgment of partial match
matcher.lookingAt()  //Judgment of whether to match from the beginning
matcher.matches()    //Judgment of perfect match

** Scientific calculator **

Note that I used a calculator function other than the standard Windows calculator for the first time.

When you want too much when you divide 101014.45 by 10000 101014.45　Mod　10000 = 1014.45