Frequency of a value in a list of entities

Question

I have an entity named Elementfisa, which contains as values (id,Post,Sarcina). Now, Post(Int Id,String Nume,String Tip) and Sarcina(Int Id,String Desc) are also entities. I have a List of all the elements I added as Elementfisa, and I want to get in a separate list the frequency of every Sarcina that every Elementfisa contains. This is my code right now:

    int nr=0;
    List<Integer> frecv=new ArrayList<Integer>();
    List<Sarcina> sarcini = new ArrayList<>();
    List<Elementfisa> efuri=findEFAll();
    for (Elementfisa i : efuri)
    {
        nr=0;
        for (Sarcina s : sarcini)
            if (s.equals(i.getSarcina()))
                    nr=1;
        if (nr==0)
        {
            int freq = Collections.frequency(efuri, i.getSarcina());
            sarcini.add(i.getSarcina());
            frecv.add(freq);
        }
    }

(findEFAll() returns every element contained in a Hashmap from a repository) But for some reason, while the sarcini list contains all the Sarcina from every Elementfisa, the frequency list will show 0 on every position. What should I change so every position should show the correct number of occurrences?

You could replace `if(nr == 0)` with `if(!sarcini.contains(i.getSarcina()))` and eliminate the `nr` code. Also, have you overridden `equals()`? — Moira, Jan 03 '17 at 18:22
No, I haven't touched equal at all, so it should use the default Java implementation — Artyomska, Jan 03 '17 at 18:24

Moira · Accepted Answer · 2017-01-03T18:34:36.720

1

You're using Collections.frequency() on efuri, a List<Elementfisa>. But you're passing i.getSarcina() to it, a Sarcina object. A List of Elementfisa cannot possibly contain a Sarcina object, so you get zero. You may have passed the wrong list to the method.

Edit:
To look at all Sarcinas in efuri, you can do this using Java 8 streams:

efuri.stream().map(element -> element.getSarcina())
    .collect(Collectors.toList()).contains(i.getSarcina())

Breakdown:

efuri.stream() //Turns this into a stream of Elementfisa
.map(element -> element.getSarcina()) //Turns this into a stream of Sarcina
.collect(Collectors.toList()) //Turn this into a list
.contains(i.getSarcina()) //Check if the list contains the Sarcina

edited Jan 03 '17 at 18:34

answered Jan 03 '17 at 18:26

Moira

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I thought that was the problem, but how can I extract from "efuri" the Sarcina, so I can compare it with i.getSarcina()? Or is there another method to compare the current i.getSarcina() with every Sarcina value from "efuri", so I can get the frequency? – Artyomska Jan 03 '17 at 18:29
@Artyomska Edited answer. – Moira Jan 03 '17 at 18:34
Thank you very much. The solution worked and now I get the correct frequency :) – Artyomska Jan 03 '17 at 18:52
@Artyomska no problem! :) – Moira Jan 03 '17 at 18:52

score 0 · Answer 2 · edited May 23 '17 at 10:29

0

Are you sure you do not need to override equals() of Elementisa? (and hashcode() too). The default Java equals() does not seem to get what you want because it would be checking the identity (not the value) of two Elementisa objects, while in your logic, two such objects with the same values may be considered as equivalent.

For more information on equals(), see

What issues should be considered when overriding equals and hashCode in Java?

edited May 23 '17 at 10:29

Community

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answered Jan 03 '17 at 18:37

leeyuiwah

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The list itself contains `Elementisa`s but they are checking if the list contains `Sarcina`s, equals wouldn't help much here – Moira Jan 03 '17 at 18:40

Frequency of a value in a list of entities

2 Answers2