Develop Reference

Why do I need to convert from Integer[] to int[]?

I have the following code
public static int[] readCSV() {
ArrayList<Integer> entries = new ArrayList<>();
try {
File file = new File("someDataFile.csv");
FileReader fr = new FileReader(file);
BufferedReader br = new BufferedReader(fr);
String line = "";
String[] row;
while((line = br.readLine()) != null) {
row = line.split(",");
for(String value : row) {
int entry = Integer.parseInt(value);
entries.add(entry);
}
}
br.close();
} catch(IOException ioe) {
ioe.printStackTrace();
}
int[] IDs = entries.toArray();
return IDs;
}
Every entry of the csv is an integer stored as a string. I get the following error: "Type mismatch: cannot convert from Object[] to int[]". As far as I understand, "entries" is not an Object[] here, it's an ArrayList<Integer>.
I was using an example given on geeksforgeeks. That didn't work and I'm not sure why.
I also checked the previous answers to the same question, and the top answer works for me. That said, I still don't have an int[], I only have Integer[]. Then I have to do this to convert from Integer[] to int[]. My question is why do I have to do all that instead of int[] IDs = entries.toArray();?
If I do
int[] IDs = new int[entries.size()];
for (int i=0; i<entries.size(); i++) {
IDs[i] = entries.get(i);
}
it works fine. Why is that different from int[] IDs = entries.toArray()?
Is there a better way to get the contents of the csv file in an int[]?

First, to answer your question, because a collection (like ArrayList) can only contain object instances. That means you must use the Integer wrapper type instead of the int primitive type. However, in Java 8+, there are simple ways to perform that conversion. I would also strongly recommend a try-with-Resources over manually closing the BufferedReader. I also simplified the code a little. Like,
public static int[] readCSV() {
List<Integer> entries = new ArrayList<>();
File file = new File("someDataFile.csv");
try (BufferedReader br = new BufferedReader(new FileReader(file))) {
String line;
while ((line = br.readLine()) != null) {
String[] row = line.split("\\s*,\\s*"); // Consume white space
for (String value : row) {
entries.add(Integer.parseInt(value));
}
}
} catch (IOException ioe) {
ioe.printStackTrace();
}
return entries.stream().mapToInt(Integer::intValue).toArray();
}

List#toArray always returns an Object[]. The closest you can get is entries.toArray(new Integer[0]) to get an Integer[].
To get an int[] you can use the Streams API or loop over the List and copy it over to an array.
Integer[] arr = list.toArray(new Integer[0]);
int[] arr2 = list.stream().mapToInt(i -> i).toArray();

How to remove specific duplicate data in array after sorting?

This is my code:
FileWriter writers = null;
try {
BufferedReader reader = new BufferedReader(new FileReader("Database.txt"));
ArrayList<Data> dataList = new ArrayList<>();
String line = "";
while ((line = reader.readLine()) != null) {
//split string and construct Data object and add it to dataList
dataList.add(parse(line));
}
reader.close();
Collections.sort(dataList);
writers = new FileWriter("final.txt");
for (Data d : dataList) {
writers.write(d.toString());
writers.write("\r\n");
}
writers.close();
} catch (Exception ex) {
ex.printStackTrace();
} finally {
}
Input/Output in this code:
input: mamy, 30, new, old
daddy, 21, new, new
output: daddy, 21,new,new
mamy , 30, new, old
Expected output:
daddy,21,new
mamy,30,new,old
My Problem is how to remove duplicate in array before storing it to final.txt? any suggestion?

I think Set is perfect for you, it eliminates duplicates.
Set<Data> dataSet = new HashSet<>(dataList);

To remove duplicates use this code right before sorting.
ArrayList<Data> newDataList = new ArrayList<>();
for (Data element : dataList) {
if (!newDataList.contains(element)) {
newDataList.add(element);
}
}
dataList = newDataList;

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 7 for correctly indexed array

I have a CSV file with 8 columns:
I have put each column into an array with the following code
public static void main(String args[]) {
List<String> wholefile = new ArrayList<String>();
List<String> id = new ArrayList<String>();
List<String> property_address = new ArrayList<String>();
List<String> first_name = new ArrayList<String>();
List<String> last_name = new ArrayList<String>();
List<String> email = new ArrayList<String>();
List<String> owner_address = new ArrayList<String>();
List<String> price = new ArrayList<String>();
List<String> date_sold = new ArrayList<String>();
Path filepath = Paths.get("./data.csv");
try {
BufferedReader br = new BufferedReader(new FileReader("./data.csv"));
String line;
while ((line = br.readLine()) != null) {
wholefile.add(line);
String[] cols = line.split(",");
id.add(cols[0]);
property_address.add(cols[1]);
first_name.add(cols[2]);
last_name.add(cols[3]);
email.add(cols[4]);
owner_address.add(cols[5]);
price.add(cols[6]);
}
System.out.println(id);
System.out.println(property_address);
System.out.println(first_name);
System.out.println(last_name);
System.out.println(email);
System.out.println(owner_address);
System.out.println(price);
} catch (IOException e) {
e.printStackTrace();
}
}
when I run this code I get the following output:
id = [id,1,2,3,4,5...]
property_address = [property address, 94032 Mockingbird Alley, 293 Haas Lane, 75 Ruskin Lane...]
and so on just like I expect!
However when I add
date_sold.add(cols[7]);
I get a error that
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 7
I do not know why as there are 8 columns and I have started indexing from 0.
Is there something wrong with my while statement ?

The version of split you're invoking removes trailing empty strings.
Trailing empty strings are therefore not included in the resulting array
Your first row has date_sold column empty. Try invoking split like this instead:
String[] cols = line.split(",", -1);

At first glance i don't see anything wrong but i guess statement for second entry line.split(",") is not considering last column which is empty. when Try to debug it with Sys.out statement and check which row is creating the problem.

Reading a text file into multiple arrays in Java

I'm currently working on a program that reads in a preset text file and then manipulates the data in various ways. I've got the data manipulation to work with some dummy data but I still need to get the text file read in correctly.
The test file looks like this for 120 lines:
Aberdeen,Scotland,57,9,N,2,9,W,5:00,p.m. Adelaide,Australia,34,55,S,138,36,E,2:30,a.m. Algiers,Algeria,36,50,N,3,0,E,6:00,p.m.(etc etc)
So each of these needs to be read into its own array, in order String[] CityName,String[] Country,int[] LatDeg,int[] LatMin,String[] NorthSouth,int[] LongDeg,int LongMin,String[] EastWest,int[] Time.String[] AMPM
So the problem is that while I'm reasonably comfortable with buffered readers, designing this particular function has proven difficult. In fact, I've been drawing a blank for the past few hours. It seems like it would need multiple loops and counters but I can't figure out the precisely how.

I am assuming that you have one city per line type of file structure. If it is not, it will require a bit of tweaking in the following solution:
I will do the following way if I am more comfortable with BufferReader as you say:
List<List<String>> addresses = new ArrayList<List<String>>();
try(BufferedReader br = new BufferedReader(new FileReader(file))) {
for(String line; (line = br.readLine()) != null; ) {
addresses.add(line.split(","));
}
}
Later, let's say you want to retrieve the country information of say 'Adelaid', you can try the following:
for (List<String> cityInfo : addresses) {
if("Adelaid".equals(cityInfo.get(0)) {
country = cityInfo.get(1);
}
}

Instead of creating different arrays (like String[] CityName,String[] Country, etc.,), try using a Domain Object.
Here, you can have a Domain object or Custom class Location with attributes
public class Location
{
private String cityName;
private String country;
private String latDeg;
etc
getters();
setters();
}`
Then you can write a file reader, each line item in the file will be a Location. So result will have
Location[] locations;
or
List locations;`

To carry out this task I should think the first thing you want to do is establish how many lines of data actually exist within the data file. You say it is 120 lines but what if it happens that it will be more or less? We would want to know exactly what it is so as to properly initialize all our different Arrays. We can use a simple method to accomplish this, let's call it the getFileLinesCount() method which will ulitmately return a Integer value that would be the number of text lines the data file holds:
private int getFileLinesCount(final String filePath) {
int lines = 0;
try{
File file =new File(filePath);
if(file.exists()){
FileReader fr = new FileReader(file);
try (LineNumberReader lnr = new LineNumberReader(fr)) {
while (lnr.readLine() != null){ lines++; }
}
}
else {
throw new IllegalArgumentException("GetFileLinesCount() Method Error!\n"
+ "The supplied file path does not exist!\n(" + filePath + ")");
}
}
catch(IOException e){ e.printStackTrace(); }
return lines;
}
Place this method somewhere within your main class. Now you need to Declare and initialize all your Arrays:
String filePath = "C:\\My Files\\MyDataFile.txt";
int lines = getFileLinesCount(filePath);
String[] CityName = new String[lines];
String[] Country = new String[lines];
int[] LatDeg = new int[lines];
int[] LatMin = new int[lines];
String[] NorthSouth = new String[lines];
int[] LongDeg = new int[lines];
int[] LongMin = new int[lines];
String[] EastWest = new String[lines];
int[] Time = new int[lines];
String[] AMPM = new String[lines];
Now to fill up all those Arrays:
public static void main(String args[]) {
loadUpArrays();
// Do whatever you want to do
// with all those Arrays.....
}
private void loadUpArrays() {
// Read in the data file.
try (BufferedReader br = new BufferedReader(new FileReader(filePath))) {
String sCurrentLine;
int x = 0;
// Read in one line at a time and Fill the Arrays...
while ((sCurrentLine = br.readLine()) != null) {
// Split each line read into an array upon itself.
String[] fileLine = sCurrentLine.split(",");
// Fill our required Arrays...
CityName[x] = fileLine[0];
Country[x] = fileLine[1];
LatDeg[x] = Integer.parseInt(fileLine[2]);
LatMin[x] = Integer.parseInt(fileLine[3]);
NorthSouth[x] = fileLine[4];
LongDeg[x] = Integer.parseInt(fileLine[5]);
LongMin[x] = Integer.parseInt(fileLine[6]);
EastWest[x] = fileLine[7];
Time[x] = Integer.parseInt(fileLine[8]);
AMPM[x] = fileLine[9];
x++;
}
br.close();
}
catch (IOException ex) { ex.printStackTrace(); }
}
Now, I haven't tested this, I just quickly punched it out but I think you can get the jest of it.
EDIT:
As #Mad Physicist has so graciously pointed out within his comment below, a List can be used to eliminate the need to count file lines therefore eliminating the need to read the data file twice. All the file lines can be placed into the List and the number of valid file lines can be determined by the size of the List. Filling of your desired arrays can now also be achieved by iterating through the List elements and processing the data accordingly. Everything can be achieved with a single method we'll call fillArrays(). Your Arrays declaration will be a little different however:
String[] CityName;
String[] Country;
int[] LatDeg;
int[] LatMin;
String[] NorthSouth;
int[] LongDeg;
int[] LongMin;
String[] EastWest;
String[] Time;
String[] AMPM;
public static void main(String args[]) {
fillArrays("C:\\My Files\\MyDataFile.txt");
// Whatever you want to do with all
// those Arrays...
}
private void fillArrays(final String filePath) {
List<String> fileLinesList = new ArrayList<>();
try{
File file = new File(filePath);
if(file.exists()){
try (BufferedReader br = new BufferedReader(new FileReader(file))) {
String strg;
while((strg = br.readLine()) != null){
// Make sure there is no blank line. If not
// then add line to List.
if (!strg.equals("")) { fileLinesList.add(strg); }
}
br.close();
}
}
else {
throw new IllegalArgumentException("GetFileLinesCount() Method Error!\n"
+ "The supplied file path does not exist!\n(" + filePath + ")");
}
// Initialize all the Arrays...
int lines = fileLinesList.size();
CityName = new String[lines];
Country = new String[lines];
LatDeg = new int[lines];
LatMin = new int[lines];
NorthSouth = new String[lines];
LongDeg = new int[lines];
LongMin = new int[lines];
EastWest = new String[lines];
Time = new String[lines];
AMPM = new String[lines];
// Fill all the Arrays...
for (int i = 0; i < fileLinesList.size(); i++) {
String[] lineArray = fileLinesList.get(i).split(",");
CityName[i] = lineArray[0];
Country[i] = lineArray[1];
LatDeg[i] = Integer.parseInt(lineArray[2]);
LatMin[i] = Integer.parseInt(lineArray[3]);
NorthSouth[i] = lineArray[4];
LongDeg[i] = Integer.parseInt(lineArray[5]);
LongMin[i] = Integer.parseInt(lineArray[6]);
EastWest[i] = lineArray[7];
Time[i] = lineArray[8];
AMPM[i] = lineArray[9];
}
}
catch(IOException e){ e.printStackTrace(); }
}
On another note...your Time Array can not be Integer since in data, what is considered the time contains a colon (:) which is a alpha character therefore (in case you haven't noticed) I have changed its declaration to String[]

How to read and store data from a text file in which the first line are titles, and the other lines are related data

I have a text file with 300 lines or so. And the format is like:
Name Amount Unit CountOfOrder
A 1 ml 5000
B 1 mgm 4500
C 4 gm 4200
// more data
I need to read the text file line by line because each line of data should be together for further processing.
Now I just use string array for each line and access the data by index.
for each line in file:
array[0] = {data from the 'Name' column}
array[1] = {data from the 'Amount' column}
array[2] = {data from the 'Unit' column}
array[3] = {data from the 'CountOfOrder' column}
....
someOtherMethods(array);
....
However, I realized that if the text file changes its format (e.g. switch two columns, or insert another column), it would break my program (accessing through index might be wrong or even cause exception).
So I would like to use the title as reference to access each column. Maybe HashMap is a good option, but since I have to keep each line of data together, if I build a HashMap for each line, that would be too expensive.
Does anyone have any thought on this? Please help!

you only need a single hash map to map your column names to the proper column index. you fill the arrays by indexing with integers as you did before, to retrieve a column by name you'd use array[hashmap.get("Amount")].

You can read the file using opencsv.
CSVReader reader = new CSVReader(new FileReader("yourfile.txt"), '\t');
List<String[]> lines = reader.readAll();
The fist line contains the headers.

you can read each line of the file and assuming that the first line of the file has the column header you can parse that line to get all the names of the columns.
String[] column_headers = firstline.split("\t");
This will give you the name of all the columns now you just read through splitting on tabs and they will all line up.

You could do something like this:
BufferedReader in = new BufferedReader(new InputStreamReader(
new FileInputStream(FILE)));
String line = null;
String[] headers = null;
String[] data = null;
Map<String, List<String>> contents = new HashMap<String, List<String>>();
if ((line = in.readLine()) != null) {
headers = line.split("\t");
}
for(String h : headers){
contents.put(h, new ArrayList<String>());
}
while ((line = in.readLine()) != null) {
data = line.split("\t");
if(data.length != headers.length){
throw new Exception();
}
for(int i = 0; i < data.length; i++){
contents.get(headers[i]).add(data[i]);
}
}
It would give you flexibility, and would only require making the map once. You can then get the data lists from the map, so it should be a convenient data structure for the rest of your program to use.

This will give you individual list of columns.
public static void main(String args[]) throws FileNotFoundException, IOException {
List<String> headerList = new ArrayList<String>();
List<String> column1 = new ArrayList<String>();
List<String> column2 = new ArrayList<String>();
List<String> column3 = new ArrayList<String>();
List<String> column4 = new ArrayList<String>();
int lineCount=0;
BufferedReader br = new BufferedReader(new FileReader("file.txt"));
try {
StringBuilder sb = new StringBuilder();
String line = br.readLine();
String tokens[];
while (line != null) {
tokens = line.split("\t");
if(lineCount != 0)
{
int count = 0;
column1.add(tokens[count]); ++count;
column2.add(tokens[count]); ++count;
column3.add(tokens[count]); ++count;
column4.add(tokens[count]); ++count;
continue;
}
if(lineCount==0){
for(int count=0; count<tokens.length; count++){
headerList.add(tokens[count]);
lineCount++;
}
}
}
} catch (IOException e) {
} finally {
br.close();
}
}

using standard java.util.Scanner
String aa = " asd 9 1 3 \n d -1 4 2";
Scanner ss = new Scanner(aa);
ss.useDelimiter("\n");
while ( ss.hasNext()){
String line = ss.next();
Scanner fs = new Scanner(line);
System.out.println( "1>"+ fs.next()+" " +fs.nextInt() +" " +fs.nextLong()+" " +fs.nextBigDecimal());
}
using a bunch of hashmap's is ok...i won't be afraid ;)
if you need to process a lot of data...then try to translate your problem into a dataprocessing transformation
for example:
read all of you data into a hashmap's, but store them in a database using some JPA implementation....then you can go round'a'round your data ;)\