how to get values from an ArrayList<Hashtable<String, ArrayList<String>>>

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

Did you build the ArrayList<Hashtable<String, ArrayList<String>>> yourself? If so, it's the wrong data structure (effectively a "parallel arrays" structure). You should define a class to hold one line of input as an object. — Jim Garrison
– Jim Garrison, Commented Apr 28, 2016 at 15:24
As @JimGarrison said, you should reconsider your data structure. — soufrk
– soufrk, Commented Apr 28, 2016 at 15:51
Hi, thanks to all for your quick responses. Actually I didn't build this structure completely by myself. However I understand your comments about creating a class, and this probably will be my next step as I am currently learning about the objects phylosophy — Cristian Muñoz
– Cristian Muñoz, Commented Apr 29, 2016 at 9:22

Hitesh Sahu · Accepted Answer · 2016-04-28 15:50:25Z

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

answered Apr 28, 2016 at 15:50

Hitesh Sahu

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Cristian Muñoz Over a year ago

Thanks for your response Hitesh. I solved it by using the values instead of keySet. However your response was useful to me in order to get the values.

OneCricketeer · Accepted Answer · 2016-04-28 15:47:27Z

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.

edited Apr 28, 2016 at 15:47

OneCricketeer

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answered Apr 28, 2016 at 15:30

Manu AG

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Comments

Cristian Muñoz · Accepted Answer · 2016-04-29 09:27:44Z

1

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!!

answered Apr 29, 2016 at 9:27

Cristian Muñoz

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2 Comments

Valentin Over a year ago

This is very fragile since order is not guaranteed in Hashtable. Instead of accessing the values list by copying the collection returned by Hashtable.values() in an ArrayList and accessing these by index, you should prefer to access it this way: processedFilesArray.get(i).get("Psals"). Ideally, if you want to process all the elements in the Hashtable, you should use Manu AG's answer.

Cristian Muñoz Over a year ago

Thanks Valentin, it works better than my solution. I also agree with you in relation with Manu AG's solution.

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