getCategoryCounts() help

The logic, written in everyday English is like this (I think!):

1. Create a Map of the type HashMap to hold our keys (the different categories) and the values (how many times each category appears).

2. Start a loop going through each of the BlogPosts that are in our array of BlogPosts (which is known in this Blog class as mPosts).

3. Get the category (as a string) for the BlogPost that you are dealing with in this round of the loop (using the getCategory() method we have already defined).

4. Create an integer variable ('count') to store the result of a check inside the Map we created at step 1, to see if the category we are dealing with is already in there (use the .get() method on our Map using the category we are dealing with as the variable passed to the method - we want to see how many times this category appears in the Map i.e. what the 'value' for this key already is).

5. If the category we are dealing with is not already in the Map (i.e. the result of the check comes back as null), set 'count' to zero (i.e. give it a zero value rather than just 'null' which is not an integer).

6. Otherwise (i.e. if it does already appear), increment the 'count' variable by 1, because we have got a repeated category and we need to increase the value already held in the Map by one.

7. 'Put' the category we are working with back into the Map together with the value stored in our 'count' variable (which will either be zero - Step 5 - or the existing value plus one - Step 6).

8. Close the loop (so that it will now go back to step 2 to start again on the next BlogPost in our mPosts array).

9. Finally, once the loop has finished going through the individual BlogPosts in our array, 'return' the Map we have created.

I got stuck on step 3 - I didn't see how easy it was to work out how many time we had already come across the category before in our loop. I hope explaining it in ordinary language helps a bit (subject to being told by Ken or Craig that I've got it wrong!!).

Good luck!

Ben

Devin;

Okay, next step then...

We have our function defined and now just need to put a bunch of code in there that does what we need, right? Here is the outline of the approach I took.

1. Define a Map variable to put in our category counts, Map<String, Integer> categoryCounts = // some sort of interface for Map.
2. Implement a for loop that goes through our blog posts you could use something like (BlogPost post : mPosts).
3. Get our category, which should be a string. Using the above syntax we could use post and the getCategory() method.
4. Count the categories in our Map and increment a counter based on their number.
5. Return our map.
6. Important! Remember to add any new import statements.

Give it another go and post back with your code if you are still stuck.

Ken

I'm still confused about the integer part.

Integer count = categoryCounts.get(category);

How is it that we get a count of the total number of categories? The HashMap categoryCounts is at the time of creation empty right? So how does it return anything to the Integer count? It is also my understanding that the get() method returns the value of its key. How is this indicative of the total number of categories? I am sure something is going completely over my head... :'(

Devin;

Let's take a look:

Task 1

In Blog.java add a new method called getCategoryCounts. It should return a Map of category to count calculated by looping over all the posts.

Okay, in our new method, getCategoryCounts() we need it to return a category mapped to the number in that category, correct? The output in key/value pairs will wind up being a programmatic representation of something like:

Dogs, 3

Cats, 4

Horses, 17

That looks like we need our map to be a <String, Integer> as a return type therefore our cookie-cutter method definition will be:

public Map<String, Integer> getCategoryCounts() {

    return null;   // Ultimately needs to return a Map<String, Integer>
}

Inside our function then, we need to define a new Map so that we can return it and then loop through our categories, count them, and add the category and count to our map.

Without giving away the entire challenge, does that give you enough to go on to proceed?

Post back if you are still stuck.

Ken

Hello ! This is my getCategoryCounts method, I feel like i'm in the right direction but I still miss something, may I have any help? Thanks!

public Map<String, Integer> getCategoryCounts() {
    Map<String, Integer> categoryCounts = new HashMap<String, Integer>();
    for (BlogPost post : mPosts) {
       if ( counter == null ) {
          counter = 0; 
        }
       counter ++;
       categoryCounts.put(post.getCategory(),counter);   
    } 
    return categoryCounts;
}

Ken, GREAT STEP BY STEP EXPLANATION! I did have to go back to add a few symbols that I missed. FYI to Others, be aware of the very last bracket } that should be to the far left.

Great explanation. For some reason I am getting the error

./com/example/BlogPost.java:49: error: cannot find symbol for (BlogPost post : mPosts) { ^ symbol: variable mPosts location: class BlogPost Note: JavaTester.java uses unchecked or unsafe operations. Note: Recompile with -Xlint:unchecked for details. 1 error

I solved it like this:

  public Map<String,Integer> getCategoryCounts () {
    Map<String,Integer> categories = new TreeMap<String,Integer>();
    Set<String> category = new TreeSet<String>();
    int count = 0;
    for (BlogPost post: mPosts){
      category.add(post.getCategory());
    }
    for (String categ: category){
      int categoryQuantity = 0;
      for (BlogPost post: mPosts){
        if(categ.equalsIgnoreCase(post.getCategory())){
          categoryQuantity++;
        }
      }
      categories.put(categ,categoryQuantity);
      count++;
    }
    return categories;
  }

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Good day, Everyone.

I have come across an interesting bug in this code challenge. When checking my work I get the following error:

"Bummer: For category Entertainment, expected 1 but received 1."

this is the code I used in my getCategoryCounts() method:

public Map<String, Integer> getCategoryCounts(){

    // Store a String as the key and an Integer as the value in a Map
    Map<String, Integer> catCount = new HashMap<String, Integer>();
    // Loop through the List of posts
    for(BlogPost blogPost : mPosts){
        // Create new Integer object to store counts and initialise value to 1
        Integer count= new Integer(1);
        // Get the category from the post
        String category = (blogPost.getCategory());
        // Check if Category exists in the Map, if it does get the value and increment by 1
        if(catCount.containsKey(category)){
            //Get current Category Count
            count = catCount.get(category);
            //Increment the count by 1
            count++;
        }
        // Add Category and Count to the Map
        catCount.put(category,count);
    }
    // Return the Map of Category to counts
    return catCount;
}

Using a print statement:

     catCount.put(category,count);
     System.out.printf("%s  :  %d%n",category,count); 

to debug the category and counts after being add to the map I get the following:

Tech : 1 Tech : 2 Science : 1 Health : 1 Health : 2 Food : 1 Entertainment : 1 Tech : 3 Food : 2 Health : 3

I also checked the Maps content using a forEach loop to print the returned Map before the return statement is executed:

    for(Map.Entry<String, Integer> entry : catCount.entrySet()){
             System.out.printf("%s : %d%n", entry.getKey(), entry.getValue());
    }
    // Return the Map of Category to counts
    return catCount;

I get the following:

Tech : 3
Entertainment : 1 Health : 3 Science : 1 Food : 2