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From: =?UTF-8?Q?Arne_Vajh=c3=b8j?= <arne@vajhoej.dk>
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Subject: Re: DeDup an ArrayList
Date: Thu, 4 Aug 2016 22:41:18 -0400
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On 8/4/2016 10:05 PM, Andreas Leitgeb wrote:
> Roedy Green <inquiry@mindprod.com> wrote:
>> This looks like trivial task, but every time I work on it, it keeps
>> ballooning in complexity.
>>
>> I wish to deDup an ArrayList.  Any two strings equalIgnoreCase are
>> considered dups. One should be removed.  The order of the items should
>> be otherwise be undisturbed.
>>
>> Part of the trouble is removing an element from an ArrayList makes you
>> lose track of where you are.
>
> Copy to a LinkedHashMap (using the toUpperCase()'d string as key, and
> the original String as value), and finally copy back to a new ArrayList...
>
> The LinkedHashMap will take care of maintaining the ordering, except
> of course, where dups are left out.

import java.util.ArrayList;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.stream.Collectors;

public class ListDeDup {
	public static void main(String[] args) {
		List<String> lst = new ArrayList<>();
		lst.add("Aa");
		lst.add("Bb");
		lst.add("Cc");
		lst.add("cC");
		lst.add("bB");
		lst.add("aA");
		System.out.println(lst);
		List<String> res = lst.stream().collect(Collectors.toMap(o -> 
o.toLowerCase(), o -> o, (o1,o2) -> o1, 
LinkedHashMap::new)).values().stream().collect(Collectors.toList());
		System.out.println(res);
	}
}

> Not sure if hashing on the uppercase version of a String is strictly
> equivalent to pairwise equalIgnoreCase, though. Maybe not, maybe close
> enough, maybe exactly same...  The performance advantage (from n-squared
> to roughly n) might be worth a little slack in some corner cases.

There is always the "Turkish problem", but ...

Arne