Thread: Using the count element method to count the occurrence of characters in an array

Hello guys,

I have an array with the following characters {'E', 'L','E','P','H','A','N','T','P','O'}

now, I need an array that will store the first array such that only the occurence occurs e.g {'E','L','P','H','A','N','T','O'}
Notice that the characters 'E' and 'P' occur twice and as a result were not repeated the second time in the new array.

How would one go about this using the counting elements technique?

I tried this but not sure how to use the counting elements technique.

char [] arr = new char{'E', 'L','E','P','H','A','N','T','P','O'};
char[] bucket = new char[(arr[0] * arr.length)];
for (int i = 0; i < len; i++)
bucket[arr[i]]++;

I honestly don't know how it works except it a technique used to count the number of occurrence of numbers.. so given an array with numbers{0,1,2,1,3,3,2,1,1}
the counting technique will work thus:
count[0] == 0(since the initial array had only 1 occurrence of 0)
count[1] == 4(number 1 occured 4 times in the original array)
count[2] ==2(occurred twice)
count[3] ==3(occured 3)

in the end, the length of the count is equal to the length of the number of the unique numbers ignoring how many times they occur.

I don't know if this could be used for characters instead of numbers, which is what I am trying to replicate using the counting element technique.

Hi,

so, could you write a small java code to use the counting element technique on numbers? I could then try to modify it for the alphabets. The problem I am having is how to successfully initialize the bucket array. In my code given below :

int [] arr = new int {1,2,3,3,3,2,1,2};
int[] bucket = new int[(arr[0] * arr.length)];
for (int i = 0; i < len; i++)
bucket[arr[i]]++;

When I tested this code framgment, It breaks because, I might have done the bucket array initialization wrongly. If you could help with how to properly initialize the bucket, I think I can handle the rest.

Using an array 'bucket' to count the frequency of occurrence of certain items requires the array to be the same size as the number of unique items being counted. For example, if the items being counted are the digits 0 - 9, then the size of the frequency array would be 10. If the items being counted are lowercase characters, then the size of the array would be 26.

If you want to size the 'bucket' to the be the same as the number of unique items in the range of items being counted, then you'll first need to determine the number of unique items. For the first example you gave, the size would be 8 for the unique characters 'E', 'L', 'P', 'H', 'A', 'N', 'T', 'O'. Your first task may be to determine the number of unique items, and a Set can be used to accomplish that.

Another approach is to size the array 'bucket' to be the largest needed (26 again for capital letters) and only report the resulting elements with values greater than zero. This approach accomplishes 2 things: determines the number of unique items AND the frequency of each of the items.

The thinking behind your sizing is not clear. Perhaps you could explain:

int[] bucket = new int[(arr[0] * arr.length)];

Hi,

I have tried some of the suggestions you gave but unfortunately, when I debug my code, I don't see anything happening.

int[] bucket = new int[9] in the case of an array with 8 elements.

then when i tried this :

for i->8
bucket[arr[i]]++;
end for loop

this should simply be adding up all the numbers in the array. so, if i = 0, it stores 0 in index 0 and 1 in index 1 and just adds the number of times it encouters 1. for an array having characters, I think this might be the way to go about it:

for i-->8
char s = arr.charAt(i);
int i = s-'a'; //convert the character to a digit
bucket[arr[i]]++;
end for loop

I don't know if this is correct way to try this out with a character array using the counting elements. My most worrying concern now is even when I try the counting element with numbers, I still don't get the right results.

Hi,
Ok, using information from you and the other friends on the thread, I have been able to get so so close to my goal. The code below is used to convert each character into an integer that is now stored in the bucket .

int len = arr.length;
int[] bucket = new int[26+1];
for(int i = 0; i<26;++i){
if(i<arr.length)
bucket[arr[i]-'a']++;
}

This gives me the following value in the bucket:

[1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0]

The respective array I used had the value ['k','i','s', 's','a'].
so, 1 a, 1 k, 1 i and 2 s. The next thing I want to get now is how to convert the digit array back to characters. Any help on this?

Thanks alot. I am grateful.