如何从ArrayList获取值 <Hashtable<String, ArrayList<String> &gt;&gt;

Question

I have a function that is capable to read data from multiple files with the following structure:

id  date    temp    psal
1   2016/02/01  37.6    35.9
2   2016/02/02  30.3    35.7
3   2016/02/03  28.2    36.8
4   2016/02/04  27.7    37.7
5   2016/02/05  28.7    37.9
6   2016/02/06  28.7    37.9

The function is:

ArrayList<Hashtable<String, ArrayList<String>>> processedFilesArray = ReadFiles(files);

If I try to retrieve the data by using for example:

System.out.println(processedFilesArray.get(0));

Then I get the following response:

{Psals=[35.9, 35.7, 36.8, 37.7, 37.9, 37.9], Temps=[37.6, 30.3, 28.2, 27.7, 28.7, 28.7], ids=[1, 2, 3, 4, 5, 6], DateStrings=[2016/02/01, 2016/02/02, 2016/02/03, 2016/02/04, 2016/02/05, 2016/02/06]}

My question is: How can I obtain the different values of the keys (Temps, Psals, ids, etc) by sepparate to plot them using jfreechart?

Thanks in advance

Answer 1

You can obtain the keys and values by this way:

//Each hastTable of proccesedFilesArray
     for(Hashtable<String,ArrayList<String>> processedFile : processedFilesArray){
        //Each entrySet of proccesedFile
        for(Entry<String, ArrayList<String>> entry : processedFile.entrySet()){
            //Filter here by key or value with if conditions
            String key = entry.getKey();
            ArrayList<String> listValue = entry.getValue();//List of Strings
            for(String value : listValue){
               //each value per hashtable key
            }

        }
    }

I dont really know how do you want to work with this but that could be a way to iterate your list and get the values of each record.

Answer 2

You can get list of keys in your Hashtable by method keySet() , which return Set of Keys.

You can convert Set to Array list like this :-

ArrayList keyList = new ArrayList(processedFilesArray.get(0).keySet());

More about keySet http://www.tutorialspoint.com/java/util/hashmap_keyset.htm

Answer 3

I finally solved this issue following Hitesh response, by using:

ArrayList keyList = new ArrayList(processedFilesArray.get(1).values());
    System.out.println(keyList.get(0));

This returns me the first group (Psals) from the second file read:

    [35.9, 35.7, 36.8, 37.7, 37.9, 37.9]

Thank you guys for your help!!