add Array::dedup_consecutive for removing consecutive repeated elements in array

[tonyfettes]

For backward compatibility, this PR updates the documentation for Array::dedup, so that it shall not break any existing code that use this function. This PR also add another function (Array::unique) to implement the originally proposed functionality, i.e. de-duplication of consecutive repeated elements.

cc @Demonmasterlqx

close #1061

Implementation in other programming language

Language	Consecutive	Non-consecutive
C++	unique	N/A
Rust	dedup	unique
NumPy	N/A	unique
JavaScript	N/A	N/A
Python	N/A	N/A
Scala	N/A	distinct
*nix	uniq	N/A
Haskell	N/A	Data.List.Unique

See more on https://rosettacode.org/wiki/Remove_duplicate_elements

Algorithm Complexity

For the time-complexity of removing non-consecutive duplications:

There are basically three approaches seen here:

• Put the elements into a hash table which does not allow duplicates. The complexity is O(n) on average, and O(n^2) worst case. This approach requires a hash function for your type (which is compatible with equality), either built-in to your language, or provided by the user.
• Sort the elements and remove consecutive duplicate elements. The complexity of the best sorting algorithms is O(n * log(n)). This approach requires that your type be "comparable", i.e., have an ordering. Putting the elements into a self-balancing binary search tree is a special case of sorting.
• Go through the list, and for each element, check the rest of the list to see if it appears again, and discard it if it does. The complexity is O(n^2). The up-shot is that this always works on any type (provided that you can test for equality).

quoted from https://rosettacode.org/wiki/Remove_duplicate_elements

Removing consecutive duplications should only require Eq trait and of O(n) time complexity.

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[peter-jerry-ye-code-review]

Potential Issues in the Provided git diff Output

1. Documentation Update Inconsistency:

   • The original comment for the dedup function was corrected from "consecutive repeated elements" to "repeated elements", which seems to be a typo correction. However, the new function dedup_consecutive was added with a comment that correctly states it removes "consecutive repeated elements". This inconsistency in the documentation might cause confusion for users.
   • Suggestion: Ensure that the documentation for both dedup and dedup_consecutive is clear and correctly reflects their functionalities. The comment for dedup should be updated to clarify that it removes all repeated elements, not just consecutive ones, if that is indeed the case.

2. Possible Infinite Loop in dedup_consecutive:

   • In the dedup_consecutive function, the while loop condition while i + 1 < self.length() && self[i] == self[i + 1] checks for consecutive duplicates and removes the second occurrence. However, if there are more than two consecutive duplicates, removing one might not move the index i forward, potentially causing an infinite loop if the array continuously has consecutive duplicates at the same index after removal.
   • Suggestion: Adjust the loop to ensure that i is incremented or the removal logic is adjusted to handle multiple consecutive duplicates more effectively.

3. Test Coverage for Edge Cases:

   • The test cases added for dedup_consecutive cover typical scenarios and some edge cases like an empty array and an array with no duplicates. However, it lacks a test case for a large array with multiple groups of consecutive duplicates, which could stress-test the efficiency and correctness of the function.
   • Suggestion: Add a test case that includes a large array with various patterns of consecutive duplicates to ensure the function handles large inputs efficiently and correctly.

These observations focus on potential issues related to documentation clarity, logical correctness, and test coverage, which are crucial for maintaining code quality and user understanding.

[coveralls]

Pull Request Test Coverage Report for Build 3307

Details

• 3 of 3 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.01%) to 83.218%

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Totals
Change from base Build 3301:	0.01%
Covered Lines:	4091
Relevant Lines:	4916

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💛 - Coveralls

[hackwaly]

Just my opinion: unique is not a good name for "removing consecutive repeated elements in array". How about keep dedup for consecutive=true and unique for consecutive=false.

[bobzhang]

note the original dedup is terribly inefficient (called too many remove), but it is qutie common API. (good first issue)
The unique API here is not very common, what are the use cases? if we want to call unique, we generally do such things:

[...@hashset.from_iter()]

[tonyfettes]

@bobzhang using

[...@hashset.from_iter()]

has roughtly the same behavior as the Array::dedup, not Array::unique, as it will only keep one of the repeated elements.

For example, for array [3, 4, 5, 6, 6, 4, 4],

• Array::dedup

  [3, 4, 5, 6]
  

• [...@hashset.from_iter()]

  [6, 3, 4, 5]
  

• Array::unique

  [3, 4, 5, 6, 4]
  

Additionally, using [...@hashset.from_iter()] discards the order that these elments has in the array, which might not be what the user would expect.

[tonyfettes]

Just my opinion: unique is not a good name for "removing consecutive repeated elements in array". How about keep dedup for consecutive=true and unique for consecutive=false.

IMO neither of the two names are good for a function that removes consecutive repeated elements, I'm considering using a longer name (like dedup_consecutive) for it.