Develop Reference

Split lines with "," and do a trim on every element [duplicate]

This is some code that I found to help with reading in a 2D Array, but the problem I am having is this will only work when reading a list of number structured like:
73
56
30
75
80
ect..
What I want is to be able to read multiple lines that are structured like this:
1,0,1,1,0,1,0,1,0,1
1,0,0,1,0,0,0,1,0,1
1,1,0,1,0,1,0,1,1,1
I just want to essentially import each line as an array, while structuring them like an array in the text file.
Everything I have read says to use scan.usedelimiter(","); but everywhere I try to use it the program throws straight to the catch that replies "Error converting number". If anyone can help I would greatly appreciate it. I also saw some information about using split for the buffered reader, but I don't know which would be better to use/why/how.
String filename = "res/test.txt"; // Finds the file you want to test.
try{
FileReader ConnectionToFile = new FileReader(filename);
BufferedReader read = new BufferedReader(ConnectionToFile);
Scanner scan = new Scanner(read);
int[][] Spaces = new int[10][10];
int counter = 0;
try{
while(scan.hasNext() && counter < 10)
{
for(int i = 0; i < 10; i++)
{
counter = counter + 1;
for(int m = 0; m < 10; m++)
{
Spaces[i][m] = scan.nextInt();
}
}
}
for(int i = 0; i < 10; i++)
{
//Prints out Arrays to the Console, (not needed in final)
System.out.println("Array" + (i + 1) + " is: " + Spaces[i][0] + ", " + Spaces[i][1] + ", " + Spaces[i][2] + ", " + Spaces[i][3] + ", " + Spaces[i][4] + ", " + Spaces[i][5] + ", " + Spaces[i][6]+ ", " + Spaces[i][7]+ ", " + Spaces[i][8]+ ", " + Spaces[i][9]);
}
}
catch(InputMismatchException e)
{
System.out.println("Error converting number");
}
scan.close();
read.close();
}
catch (IOException e)
{
System.out.println("IO-Error open/close of file" + filename);
}
}

I provide my code here.
public static int[][] readArray(String path) throws IOException {
//1,0,1,1,0,1,0,1,0,1
int[][] result = new int[3][10];
BufferedReader reader = new BufferedReader(new FileReader(path));
String line = null;
Scanner scanner = null;
line = reader.readLine();
if(line == null) {
return result;
}
String pattern = createPattern(line);
int lineNumber = 0;
MatchResult temp = null;
while(line != null) {
scanner = new Scanner(line);
scanner.findInLine(pattern);
temp = scanner.match();
int count = temp.groupCount();
for(int i=1;i<=count;i++) {
result[lineNumber][i-1] = Integer.parseInt(temp.group(i));
}
lineNumber++;
scanner.close();
line = reader.readLine();
}
return result;
}
public static String createPattern(String line) {
char[] chars = line.toCharArray();
StringBuilder pattern = new StringBuilder();;
for(char c : chars) {
if(',' == c) {
pattern.append(',');
} else {
pattern.append("(\\d+)");
}
}
return pattern.toString();
}

The following piece of code snippet might be helpful. The basic idea is to read each line and parse out CSV. Please be advised that CSV parsing is generally hard and mostly requires specialized library (such as CSVReader). However, the issue in hand is relatively straightforward.
try {
String line = "";
int rowNumber = 0;
while(scan.hasNextLine()) {
line = scan.nextLine();
String[] elements = line.split(',');
int elementCount = 0;
for(String element : elements) {
int elementValue = Integer.parseInt(element);
spaces[rowNumber][elementCount] = elementValue;
elementCount++;
}
rowNumber++;
}
} // you know what goes afterwards

Since it is a file which is read line by line, read each line using a delimiter ",".
So Here you just create a new scanner object passing each line using delimter ","
Code looks like this, in first for loop
for(int i = 0; i < 10; i++)
{
Scanner newScan=new Scanner(scan.nextLine()).useDelimiter(",");
counter = counter + 1;
for(int m = 0; m < 10; m++)
{
Spaces[i][m] = newScan.nextInt();
}
}

Use the useDelimiter method in Scanner to set the delimiter to "," instead of the default space character.
As per the sample input given, if the next row in a 2D array begins in a new line, instead of using a ",", multiple delimiters have to be specified.
Example:
scan.useDelimiter(",|\\r\\n");
This sets the delimiter to both "," and carriage return + new line characters.

Why use a scanner for a file? You already have a BufferedReader:
FileReader fileReader = new FileReader(filename);
BufferedReader reader = new BufferedReader(fileReader);
Now you can read the file line by line. The tricky bit is you want an array of int
int[][] spaces = new int[10][10];
String line = null;
int row = 0;
while ((line = reader.readLine()) != null)
{
String[] array = line.split(",");
for (int i = 0; i < array.length; i++)
{
spaces[row][i] = Integer.parseInt(array[i]);
}
row++;
}
The other approach is using a Scanner for the individual lines:
while ((line = reader.readLine()) != null)
{
Scanner s = new Scanner(line).useDelimiter(',');
int col = 0;
while (s.hasNextInt())
{
spaces[row][col] = s.nextInt();
col++;
}
row++;
}
The other thing worth noting is that you're using an int[10][10]; this requires you to know the length of the file in advance. A List<int[]> would remove this requirement.

Filling a double[][] from the CSV file

I have this CSV file:
World Development Indicators
Number of countries,4
Country Name,2005,2006,2007,2008,2009,2010,2011,2012,2013,2014
Bangladesh,6.28776238,13.20573922,23.46762823,30.16828408,34.35334451,44.94535882,55.19256723,62.82023906,74.42964608,80.03535051
"Bahamas, The",69.21279415,75.37855087,109.340767,102.7875065,101.2186453,118.8292307,81.5628489,80.65383375,76.05187427,82.29635806
Brazil,46.31418452,53.11025849,63.67475185,78.5549801,87.54187651,100.8810115,119.0023853,125.0018521,135.3050481,138.9514906
Germany,94.55486999,102.2828888,115.1403608,126.5575074,126.2280577,106.4836959,109.6595675,111.5940398,120.9211651,120.4201855
I am trying to store countries' data(double once) into a matrix(double[][]). Here is the code that I have so far:
public double[][] getParsedTable() throws IOException {
double[][] table = new double[4][10];
String row;
int indexRow = 0;
int indexColumn = 0;
BufferedReader br = new BufferedReader(new FileReader(fileName));
br.readLine();
br.readLine();
String line = br.readLine();
while(line != null && !line.isEmpty()){
line = br.readLine();
String[] array = line.split(",(?=(?:[^\"]*\"[^\"]*\")*[^\"]*$)", -1);
for(int i = 1; i < array.length; i++){
table[indexRow][indexColumn] = Double.parseDouble(array[i]);
indexColumn++;
}
indexColumn = 0;
indexRow++;
}
System.out.print(Arrays.deepToString(table));
return table;
}
I am getting an arror : NullPointerException at:
String[] array = line.split(",(?=(?:[^\"]*\"[^\"]*\")*[^\"]*$)", -1);
I cant figure out why. I tried different combinations. nothing seems to work. It seems to pick up the numbers from the CSV file and store them, but when I call:
System.out.print(Arrays.deepToString(table));
it does not print out anything, hence I cant check if its stored properly or not. Could you tell me: 1. Why I am getting an error. 2. Why System.out.println does not print out an array. Thanks

If we assume that name of a country will not contain a digit and country name and numbers will be only comma separated, then following can be done without regex. I have changed file reading a little bit because it can run into issues.
public double[][] getParsedTable() throws IOException {
double[][] table = new double[4][10];
int indexRow = 0;
int indexColumn = 0;
BufferedReader br = new BufferedReader(new FileReader(fileName));
br.readLine(); // ignore first line
br.readLine(); // ignore second line
br.readLine(); // ignore third line (contains title)
String line;
while (true) {
line = br.readLine();
if (line == null) break; // end of file reading
int index = 0;
while (true) {
index = line.indexOf(",", index) + 1;
if (Character.isDigit(line.charAt(index))) {
break;
}
}
// from index, line is expected to contain comma separated numbers
String[] array = line.substring(index).split(",");
for (int i = 0; i < array.length; i++) {
table[indexRow][indexColumn] = Double.parseDouble(array[i]);
indexColumn++;
}
indexColumn = 0;
indexRow++;
}
System.out.print(Arrays.deepToString(table));
return table;
}

In the csv, first 3 lines are not real country's data. So read in line-4 before while loop starts.
In while loop, first finish the processing of line string first. Eg: regular expression check & assign split data into table.
Then only read in next line at end of while loop, to be processed in next iteration.
Feel free to try this out:
public double[][] getParsedTable() throws IOException {
double[][] table = new double[4][10];
int indexRow = 0;
int indexColumn = 0;
// check whether you need to handle any exception for this
BufferedReader br = new BufferedReader(new FileReader(fileName));
String line = null;
try {
// line 1-3 are not real country's data
br.readLine();
br.readLine();
br.readLine();
// first country data begin at line 4
line = br.readLine();
} catch (IOException e) {
e.printStackTrace();
}
while (line != null && !line.isEmpty()) {
String[] array = line.split(",(?=(?:[^\"]*\"[^\"]*\")*[^\"]*$)", -1);
for (int i = 1; i < array.length; i++) {
table[indexRow][indexColumn] = Double.parseDouble(array[i]);
indexColumn++;
}
indexColumn = 0;
indexRow++;
// read next line only at end of loop, not beginning of loop
// line is ready to be processed at next iteration
try {
line = br.readLine();
} catch (IOException e) {
e.printStackTrace();
}
}
System.out.print(Arrays.deepToString(table));
return table;
}

Arrays.deepToString is wrong. You are passing in an array of primitives. When you pass it in, you pass in double[][]. This is interpeted as Object[] where the objects are double[], so it will try to print double[] objects, and not print doubles.
One solution is to create an array Double[][].
Change
double[][] table = new double[4][10];
to
Double[][] table = new Double[4][10];
Autoboxing will convert each double to a Double. Since Double is an object and not a primitive, deepToString will print out each Double individually. If you read the javadoc for deepToString it explains that it operates recursively on arrays of reference type, not on primitive arrays.
If you want to stick with double[][]
for (int i = 0; i < table.length; i++) {
for (int j = 0; j < table[i].length; j++) {
System.out.print(table[i][j]);
System.out.print(' ');
}
System.out.println();
}

Java replace characters in a TextFile - Alice In Wonderland

I'm trying to make a compressor for TextFiles and I get stuck at replacing characters.
This is my code:
compress.setOnAction(event ->
{
String line;
try(BufferedReader reader = new BufferedReader(new FileReader(newFile)))
{
while ((line = reader.readLine()) != null)
{
int length = line.length();
String newLine = "";
for (int i = 1; i < length; i++)
{
int c = line.charAt(i);
if (c == line.charAt(i - 1))
{
}
}
}
}
catch (IOException ex)
{
ex.printStackTrace();
}
});
So what I want to do is: I want to find all the words where two characters are equal, if they are aside (Like 'Took'). When the if statement is true, I want to replace the first letter of the two equals characters, so it would look like: 'T2ok'.
I've tried a lot of things and I get an ArrayOutOfbounds, StringOutOfbounds, and so on, all the time...
Hope someone has a great answer :-)
Regards

Create a method that compress one String as follows:
Loop throu every character using a while loop. Count the duplicates in another nested while loop that increments the current index while duplicates are found and skips them from being written to output. Additionally this counts their occurence.
public String compress(String input){
int length = input.length(); // length of input
int ix = 0; // actual index in input
char c; // actual read character
int ccounter; // occurrence counter of actual character
StringBuilder output = // the output
new StringBuilder(length);
// loop over every character in input
while(ix < length){
// read character at actual index then inc index
c = input.charAt(ix++);
// we count one occurrence of this character here
ccounter = 1;
// while not reached end of line and next character
// is the same as previously read
while(ix < length && input.charAt(ix) == c){
// inc index means skip this character
ix++;
// and inc character occurence counter
ccounter++;
}
// if more than one character occurence is counted
if(ccounter > 1){
// print the character count
output.append(ccounter);
}
// print the actual character
output.append(c);
}
// return the full compressed output
return output.toString();
}
Now you can use this method to create a file input to output stream using java8 techniques.
// create input stream that reads line by line, create output writer
try (Stream<String> input = Files.lines(Paths.get("input.txt"));
PrintWriter output = new PrintWriter("output.txt", "UTF-8")){
// compress each input stream line, and print to output
input.map(s -> compress(s)).forEachOrdered(output::println);
} catch (IOException e) {
e.printStackTrace();
}
If you really want to. You can remove the input file and rename the output file afterwards with
Files.move(Paths.get("output.txt"), Paths.get("input.txt"),StandardCopyOption.REPLACE_EXISTING);
I think this is the most efficient way to do what you want.

try this:
StringBuilder sb = new StringBuilder();
String line;
try(BufferedReader reader = new BufferedReader(new FileReader(newFile)))
{
while ((line = reader.readLine()) != null)
{
if (!line.isEmpty()) {
//clear states
boolean matchedPreviously = false;
char last = line.charAt(0);
sb.setLength(0);
sb.append(last);
for (int i = 1; i < line.length(); i++) {
char c = line.charAt(i);
if (!matchedPreviously && c == last) {
sb.setLength(sb.length()-1);
sb.append(2);
matchedPreviously = true;
} else matchedPreviously = false;
sb.append(last = c);
}
System.out.println(sb.toString());
}
}
}
catch (IOException ex)
{
ex.printStackTrace();
}
This solution uses only a single loop, but can only find occurrences of length 2

Longest and shortest line in text file behaving strangely

I am having some problems with my code. It is a program that reads lines from a text file and the output is the shortest and the longest string and the average size as a decimal double (x,xx). My current code is:
import java.io.*;
import java.util.*;
public class LineCalculator {
public static void main(String[] arr){
System.out.println("Enter the name of the input file");
Scanner scanner = new Scanner(System.in);
String file = scanner.nextLine();
try (BufferedReader br = new BufferedReader(new FileReader(file))) {
String line;
int sum = 0;
double average = 0;
int totallength = 0;
String shortestline = new String();
String longestline = new String();
while ((line = br.readLine()) != null) {
sum++;
if (shortestline.length() > line.length()||line!=null){
shortestline = line;
}
if(longestline.length() < line.length()){
longestline = line;
}
int temp = line.length();
totallength = totallength + temp;
average = (double) Math.round(100*totallength/(double)sum)/100;
}
System.out.println("Shortest line: "+shortestline);
System.out.println("Longest line: "+longestline);
System.out.println("Average lenght of the lines: "+ average);
} catch (FileNotFoundException e) {
System.out.println("File not found, panic!");
} catch (IOException e) {
System.out.println("The input of the file is not compatible");
e.printStackTrace();
}
}
}
which works partially, it outputs the correct average and longest line, although I do not know why it outputs the correct longest line (the < sign in this code doesn't seem correct) and the shortestline always returns the latest input in the file for some reason. Can anyone see my mistake?

Look at what this code is doing. If line is shorter than shortest OR it is not null (which is every line in the file!) we set it to be the new shortest line.
if (shortestline.length() > line.length()||line!=null){
shortestline = line;
}
It should be
if (shortestline.length() > line.length()){
shortestline = line;
}
or, if you intended to do a null check:
if (line != null && shortestline.length() > line.length()){
shortestline = line;
}
Pshemo correctly pointed out another problem, which is that you initialize shortestline to be new String(), whose length is 0. You will never encounter a string with length less than 0.

Jump to specific line in .txt file where all lines are of equal length in Java

I have a text file which contains about 1 million lines of information. I'm looking for a way to jump to a specific line given that I know which line I want, and all lines are of equal length.
I read that it's possible to do so without having to read each line given that all lines are equal. If so, can anyone provide an example code of how do I do this? Or am I better off simply reading each line and looping it?

I guess you are looking for a random file access
File file = ...;
RandomAccessFile randomAccessFile = new RandomAccessFile(file, "r");
int lineNumber = ...; // first line number is 0
int lineWidth = ...; // your fixed line width
long beginIndexOfLine = lineWidth * lineNumber;
randomAccessFile.seek(beginIndexOfLine);
byte[] line = new byte[lineWidth];
randomAccessFile.read(line);

Are you looking for this:
String line = FileUtils.readLines(file).get(lineNumber);
or you may try using iterator like this:-
LineIterator l= IOUtils.lineIterator(new BufferedReader(new FileReader("file.txt")));
for (int lineNumber = 0; l.hasNext(); lineNumber++) {
String line = (String) l.next();
if (lineNumber == desiredLineNumber) {
return line;
}
}
EDIT:-
From here:-
int sizeofrecordinbytes = 290;
// for this example this is 1 based, not zero based
int recordIWantToStartAt = 12400;
int totalRecordsIWant = 1000;
File myfile = new File("someGiantFile.txt");
// where to seek to
long seekToByte = (recordIWantToStartAt == 1 ? 0 : ((recordIWantToStartAt-1) * sizeofrecordinbytes));
// byte the reader will jump to once we know where to go
long startAtByte = 0;
// seek to that position using a RandomAccessFile
try {
// NOTE since we are using fixed length records, you could actually skip this
// and just use our seekToByte as the value for the BufferedReader.skip() call below
RandomAccessFile rand = new RandomAccessFile(myfile,"r");
rand.seek(seekToByte);
startAtByte = rand.getFilePointer();
rand.close();
} catch(IOException e) {
// do something
}
// Do it using the BufferedReader
BufferedReader reader = null;
try {
// lets fire up a buffered reader and skip right to that spot.
reader = new BufferedReader(new FileReader(myfile));
reader.skip(startAtByte);
String line;
long totalRead = 0;
char[] buffer = new char[sizeofrecordinbytes];
while(totalRead < totalRecordsIWant && (-1 != reader.read(buffer, 0, sizeofrecordinbytes))) {
System.out.println(new String(buffer));
totalRead++;
}
} catch(Exception e) {
// handle this
} finally {
if (reader != null) {
try {reader.close();} catch(Exception ignore) {}
}
}