Question

I have a file that looks like this:

    1st ­ ­ ­   ­­­ 2nd ­ ­ ­   ­­­ nth
    e1­ ­ ­ ­   ­­­ ­­v1 ­ ­ ­   ­­­ 1
    e1 ­ ­ ­   ­­­ v3 ­ ­ ­   ­­­ 2
    e1 ­ ­ ­   ­­­ v4 ­ ­ ­   ­­­ 4
    e1 ­ ­ ­   ­­­ v5 ­ ­ ­   ­­­ 7
    e2 ­ ­ ­   ­­­ v1 ­ ­ ­   ­­­ 1
    . ­ ­ ­   ­ ­ ­. ­ ­ ­  ­ ­ ­­­ .
    . ­ ­ ­   ­ ­ ­. ­ ­ ­   ­­­  .
    . ­ ­ ­   ­ ­ ­.      ­  .

I want the first column to be the name of the arraylist (e1, or e2, or e3), I want the second column to have it’s value (an int), inside the nth index.

How would I go about doing that?

Id you’d like further clarification on what I mean, please don’t be afraid to leave a pm.

p.s. This is part of a bigger project, but I’m kind of stuck at the format of the data.

I’m assuming i’ll have to look for an arraylist with the the name (first column) and if i find it, then add the value (2nd column) at the nth value (3rd column), and if I don’t find it, I make an arrayList, and THEN do the aforementioned.

Update

So I managed to get the program almost working — I couldn’t use the original structure of ArrayLists because all variables have to be declared during compilation — can’t be declared after.
I decided to use a hashmap, with the key has the 1st value, and an arraylist of the 2nd values in the nth position:

`HashMap<String, ArrayList<Integer>> userRatings = new HashMap<String, ArrayList<Integer>>();
 if(!userRatings.containsKey(user)) //The user does not have ratings.
                {
                    ArrayList<Integer> ratings = new ArrayList<Integer>();
                    //                     ratings = userRatings.get(user);
                   for (int j = 0; j < 50; j++)
                    {
                        ratings.add(j);
                    }
                    userRatings.get(user).add(location,value);
}                }
                else //The user has ratings
                {
                    userRatings.get(user).add(location,value);**
                }
                System.out.println(user + " " + userRatings.get(user));
            }
            bufferReader.close();
        }    catch (FileNotFoundException e)
        {
            System.out.println("File does not exist or could not be found.");
        }
        catch (IOException e)
        {
            System.out.println("Can't read from file");
        }
        catch (NullPointerException e)
        {
        }`

The problem I now have is in adding to the arraylist. How would I do that in the bolded areas? — How would I populate and manipulate the arraylist?

Answer 1

To be honest, I think the initial problem is in reading the file in
that format.

This is easy if you use the right library. Take a look at this one: http://opencsv.sourceforge.net/, which is meant to parse csv files. From that site:

Can I use my own separators and quote characters?

Yes. There are
constructors that cater for supplying your own separator and quote
characters. Say you’re using a tab for your separator, you can do
something like this:

CSVReader reader = new CSVReader(new FileReader("yourfile.csv"), '\t');

I think this is exactly what you’re trying to do. You’re asking this library to parse the input file with tab-delimited values instead of comma-delimited. From your example above, that seems to be what your input format is.