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Looking for elegant way of searching through an array of strings for duplicate entries. Brute force method works

I have a file of alphanumeric VIN numbers from vehicles (saved as strings). I need to parse through this file and determine
1) Is a VIN duplicated? If so, how many times
2) Write the duplicated VIN and the total number of duplicates to a text file
I have gotten it to work using the brute force method dual nested For loops. Am looking for a more elegant way to parse the strings. I'm using Java 7 in NetBeans 8.2 and it doesn't appear to like using the .set or hashmap.
Constraints
1) The VINs may be in any order
2) The duplicates can be scattered through the file at random
/* a) Open input and output files
*/
try {
inputStream = new BufferedReader(new FileReader(fileName));//csv file
outputStream = new PrintWriter(new FileWriter("DuplicateVINs.txt"));
/* b) Read in file line by line
then slice out the 17 digit VIN from the extra data I don't care about
*/
while ((thisLine = inputStream.readLine()) != null) {
l = thisLine.substring(1, 18);
linesVIN.add(l.split(","));//why does this split have to be here?
}
/*c) Now that the List is full calculate its size and then write to array of strings
*/
String[][] inputArray = new String[linesVIN.size()][];
i=linesVIN.size();
System.out.println(i);
linesVIN.toArray(inputArray);
/* d) Will use two nested For loos to look for duplicates
*/
countj=0;
countk=0;
for (int j = 1;j<=i-1; j++){ //j loop
duplicateVIN=Arrays.toString(inputArray[j]);
for(int k=1;k<=i-1;k++){
if(duplicateVIN.equals(Arrays.toString(inputArray[k]))){
countk=countk+1;
foundFlag=true;
} else{
//
if(countk>=2){
//if(j!=k){
System.out.println(duplicateVIN + countk);
//} // see if removes the first duplicate
}
foundFlag=false;
countk=0;
}
} //ends k loop
countj=j;
} //ends j loop
} //Completes the try
[2q3CDZC90JH1qqqqq], 3
[2q4RC1NG1JR1qqqqq], 4
[2q3CDZC96KH1qqqqq], 2
[1q4PJMDN8KD1qqqqq], 7

I'm using Java 7 in NetBeans 8.2 and it doesn't appear to like using the .set or hashmap.
Your first step should be to figure out what you're doing wrong with a map. A hashmap is the perfect solution for this problem, and is really what you should be using.
Here's a broad example of how the solution would work, using the information you provided.
Map<String,Integer> countMap = new HashMap<String,Integer>();
while ((thisLine = inputStream.readLine()) != null) {
l = thisLine.substring(1, 18);
if(countMap.containsKey(l)){
countMap.put(l, countMap.get(l)+1);
}else{
countMap.put(l,1);
}
}
I'm assuming that the while loop your provided is properly iterating over all VIN numbers.
After this while loop is completed you would just need to output the values of each key, similar to this:
for(String vin : countMap.keySet()){
System.out.println("VIN: "+vin+" COUNT: "+countMap.get(vin));
}
If I've read your problem correctly, there is no need for a nested loop.

Counting total file lines using BufferedReader [duplicate]

This question already has answers here:
Number of lines in a file in Java
(19 answers)
Closed 4 years ago.
So basically, I'm trying to save several data saved from a file into an Array therefor I need to somehow get the size that the Array must be initialized to.
Is there any way to do that without creating another loop to count all the lines until the read line is null? Since that would require to re-open the file later which would not be very optimal. I'm trying to keep it as compact as possible.
Also, no I can't use ArrayLists.

I would go for an ArrayList, as Haroon and Hovercraft.
However, if it is not an option, why not :
// 1. Create a new Set of String
Set<String> stringSet = new HashSet<String>();
// 2. Loop through bufferedReader and add lines to set
for (String line = br.readLine(); line != null; line = br.readLine()) {
stringSet.add(line);
}
// 3. Copy set to a new array
int n = stringSet.size();
String array[] = new String[n];
array = stringSet.toArray(array);
But don't expect huge performances.

If you know in advance how many lines there will be you create the array before the loop and then you will need a counter which you use an an index into the array. You increment the counter each time through the loop.
If the number of lines is variable then add the lines to an ArrayList in the loop and then convert the ArrayList to an array after the loop

Setting two different text files as seperate string arrays and finding matches from the two arrays in Java

So basically i'm trying to take two text files (one with many jumbled words and one with many dictionary words.) I am supposed to take these two text files and convert them to two seperate arrays.
Following that, I need to compare jumbled strings from the first array and match the dictionary word in the second array up to it's jumbled counterpart. (ex. aannab(in the first array) to banana(in the second array))
I know how to set one array from a string, however I don't know how to do two from two seperate text files.

Use HashMap for matching. Where first text file data will be the key of Map and second text file data will be value. Then, by using key, you will get matching value.

you can read each file into an array like this:
String[] readFile(String filename) throws IOException {
List<String> stringList = new ArrayList<>();
try {
FileInputStream fis = new FileInputStream(new File(filename));
BufferedReader br = new BufferedReader(new InputStreamReader(fis));
String line = null;
while ((line = br.readLine()) != null) {
stringList.add(line);
}
} finally {
br.close();
}
return stringList.toArray(new String[stringList.size()]);
}
Next, try to do the matching:
String[] jumbles = readFile("jumbles.txt");
String[] dict = readfile("dict.txt);
for (String jumble : jumbles) {
for (String word : dict) {
// can only be a match if the same length
if (jumble.length() == word.length()) {
//next loop through each letter of jumble and see if it
//appears in word.
}
}
}

I know how to set one array from a string, however I don't know how to do two from two seperate text files
I would encourage you to divide your problems don't knows and knows.
Search don't knows over internet you will get lot of ways to do it.
Then search for what you know,to explore whether it can be done in a better way.
To help you here,
Your Don't knows:
Reading file in Java.
Processing the content of read file.
Your known part :
String to array representation ( Search whether there are better ways in your use case)
Combine both :-)

Get csv and compare lines. ArrayList? Java

i dont't use java very often and now i got some Problem.
I want to read a CSV file like this one:
A,B,C,D
A,B,F,K
E,F,S,A
A,B,C,S
A,C,C,S
Java don't know dynamic arrays, so i choose an ArrayList. This works so far. The Problem is:
How can I store the ArrayList? I think an other ArrayList would help.
This is what I got:
BufferedReader reader = new BufferedReader(
new InputStreamReader(this.getClass().getResourceAsStream(
"../data/" + filename + ".csv")));
List rows = new ArrayList();
String line;
while ((line = reader.readLine()) != null) {
rows.add(Arrays.asList(line.split(",")));
}
Now I get an ArrayList with a size of 5 for rows.size().
How do I get row[0][0] for example?
What do I want to do? The Problem is i want to find the same row except the last column.
For example i want to find row 0 and row 3.
thank you very much
Thank you all! You helped me a lot. =) Maybe Java and I will become friends =) THANKS!

You don't need to know the row size in advance, String.split() returns a String array:
List<String[]> rows = new ArrayList<String[]>();
String line = null;
while((line = reader.readLine()) != null)
rows.add(line.split(",", -1));
To access a specific row:
int len = rows.get(0).length;
String val = rows.get(0)[0];
Also, are you always comparing by the entire row except the last column? You could just take off the last value (line.replaceFirst(",.*?$", "")) and compare the rows as strings (have to be careful of whitespace and other formatting, of course).
A slightly different way:
Set<String> rows = new HashSet<String>();
String line = null;
while((line = reader.readLine()) != null){
if(!rows.add(line.substring(0, line.lastIndexOf(','))))
System.out.println("duplicate found: " + line);
}
Of course, modify as necessary if you actually need to capture the matching lines.

You'll need to declare an ArrayList of arrays. Asuming that csv file has a known number of columns, the only dynamic list needed here are the "rows" of your "table", formed by an ArrayList(rows) of arrays char[] (columns). (If not, then an ArrayList of ArrayList is fine).
It's just like a 2D table in any other language: an array of arrays. Just that in this case one of the arrays needs to be dynamic.
To read the file you'll need two loops. One that reads each line, just as you're doing, and another one that reads char per char.
Just a quick note: if you are going to declare an array like this:
char[] row = new char[5];
and then going to add each row to the ArrayList like this:
yourList.add(row);
You will have a list full of pointers to the same array. You'll need to use the .clone() method like this:
yourList.add(row.clone());
To access it like table[1][2], you'll need to use arraylist.get(1).get(2);

I am having trouble using FileReader to write a txt file to an array (Java), what am I doing wrong?

Scanner s = null;
try {
s = new Scanner(new BufferedReader(new FileReader("rates.txt")));
for (int i=0; i<9; i++){
while(s.hasNext()){rates[i] = s.next();}
System.out.println(rates[i]);
}
}catch (IOException e){
System.out.println(e);
}
finally {
if (s != null) {
s.close();
}
}
When I run this code, it reads the last chunk of characters in my txt file, places them in rates[0], sticks null in 1-9. I'm not sure why it's reading the end of my file first. The contents of the txt are below..
USD 1.34
EUR 1.00
JPY 126.28
GBP 0.88
INR 60.20
It reads the 60.20, which is all it is recording in the array. Any help would be appreciated. I guess I could give you the results of running this code:
run:
60.20
null
null
null
null
null
null
null
null
BUILD SUCCESSFUL (total time: 0 seconds)

while(s.hasNext()){rates[i] = s.next();}
In plain english, this says: While there are tokens left, put the next token into rates[i].
So it will put the first token into rates[i], then the next token into rates[i], then the next token into rates[i], ..., and finally the last token into rates[i]. Since i is not modified, all the values are written into the same element of the array, overwriting the previously read values.

I recommend:
Using List instead of array
More flexible, much easier to work with, takes advantage of Java Collections Framework, etc
Not storing the currency symbol and the numeric exchange rate all in one mixed bag
...but using a class to encapsulate the pair
Using Scanner.nextDouble() to read the numeric exchange rate (which presumably you'll want to convert to double anyway)
So, something like this:
List<ExchangeRate> allRates = new ArrayList<ExchangeRate>();
while (sc.hasNext()) {
String symbol = sc.next();
double rate = sc.nextDouble();
allRates.add(new ExchangeRate(symbol, rate));
}
Note how:
You no longer need to know how many elements to allocate in an array
The symbol and the rate aren't all thrown into one mixed bag
List.add means no counter that you need to keep track of and manage
i.e. the bug in your original question!

I think the problem is that line 5, which contains your while loop, reads the entire file input. So you read your entire file on the first for loop iteration where i = 0; The next time your for loop there is nothing left to read.
You probably want something like this instead:
List rates = new ArrayList();
while (s.hasNext()) {
rates.add(s.next());
}

One other potential problem: FileReader uses the platform default encoding. This can be appropriate to process user-supplied files, but if the files are part of the application, they can get corrupted when the application is run on a system with an incompatible default encoding (and no, using only ASCII characters does not protect you completely against this).
To avoid the problem, use new InputStreamReader(new FileInputStream(filename), encoding) instead - and realize that you actually have to pick an encoding for your file.