One-line Java scanner to read a matrix from a file

Question

I have been using this; A kind of one-liner:

public static String[] ReadFileToStringArray(String ReadThisFile) throws FileNotFoundException{
    return (new Scanner( new File(ReadThisFile) ).useDelimiter("\\A").next()).split("[\\r\\n]+");
}

To read a file with this type of contents(i.e. with string tokens):

abcd
abbd
dbcd

But, now my file contents are something like this:

1 2 3 4
1 2 2 4
1 5 3 7
1 7 3 8

I want these values to be read as integer.

I have seen these 1, 2 and 3 questions but they do not answer to my question.

I have tried the following but failed:

public static int[][] ReadFileToMatrix(String ReadThisFile) throws FileNotFoundException{
    return (new Scanner( new File(ReadThisFile) ).useDelimiter("\\A").nextInt()).split("[\\r\\n]+");
}

Error message: Cannot invoke split(String) on the primitive type int. I understand the message and know it's horribly wrong :)

Can anybody suggest the right way to achieve this.

P.S. With all due respect, "NO" to solutions with loops.

Its pretty easy to read the numbers as `int`s and store them in 1D array. But i cannot think of a way to convert the 1D array in 2D without a loop. Or at least recursion.. — gkrls, Mar 11 '15 at 12:05
According to Java conventions, variables (`readThisFile`) and method names (`readFileToMatrix`) are starting with lowercase letters. — gaborsch, Mar 12 '15 at 09:37
You can google for "Java Naming Conventions", but here's a brief: http://en.wikipedia.org/wiki/Naming_convention_%28programming%29#Java — gaborsch, Mar 12 '15 at 10:38

score 1 · Answer 1 · answered Mar 11 '15 at 11:38

1

Seems like an over complication of using classes when a basic BufferedReader with Integer.parseInt(line.split(" ")[n]); will do.

answered Mar 11 '15 at 11:38

TV Trailers

25
4

Could you kindly write the complete line? how will it go after `return`? – tod Mar 11 '15 at 11:52
Not in one line. Why do you need it on one line? – TV Trailers Mar 11 '15 at 21:39

score 0 · Answer 2 · answered Mar 12 '15 at 09:31

If you use Java 7 or higher you can use something like this. I cannot think of a way to do it in one line without a loop. Just put this into a methode and call it.

//Read full file content in lines
List<String> lines = Files.readAllLines(path, StandardCharsets.UTF_8);

int NR_OF_COLUMNS = 4;
int NR_OF_ROWS = lines.size();

int[][] result = new int[NR_OF_ROWS][NR_OF_COLUMNS];

for(int rowIndex = 0; rowIndex < NR_OF_ROWS; rowIndex++)
{
    String[] tokens = lines.get(rowIndex).split("\\s+");  //split every line
    for(int columnIndex = 0; columnIndex < NR_OF_COLUMNS; columnIndex++)
        result[rowIndex][columnIndex] = Integer.parseInt(tokens[columnIndex]);   //convert every token to an integer
}
return result;

score 0 · Answer 3 · answered Mar 12 '15 at 09:51

0

With Java 8, you can use Lambdas:

public static int[][] readFileToMatrix(String readThisFile) throws FileNotFoundException{
    return Arrays.stream((new Scanner( new File(readThisFile) ).useDelimiter("\\A").nextInt()).split("[\\r\\n]+")).mapToInt(Integer::parseInt).toArray();
}

Otherwise you cannot do it without a loop. You have a String[] array, and you want to call Integer.parseInt() for each element, one by one.

answered Mar 12 '15 at 09:51

gaborsch

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Looks good, could you please add the detail of how it will map and then it will be returned back as an `int` 2D array. – tod Mar 12 '15 at 10:09

One-line Java scanner to read a matrix from a file

3 Answers3