Java Alphabetically Sort ArrayLists inside an ArrayList

Question

I have this ArrayList, that contains other ArrayLists

Original: [[EHM, Evans, 45], [AB, Evans, 63], [J, Jones, 72], [RA, Jones, 85], [B, Smith, 55]]

I'd like to sort this ArrayList in alphabetical order, to give this output

Desired: [[AB, Evans, 63], [B, Smith, 55], [EHM, Evans, 45], [J, Jones, 72], [RA, Jones, 85]]

This data is based on a textfile that i'm importing, so may change. I want to compare position 0 in each ArrayList and sort alphabetically. Currently the original list sits within a variable 'multiMarkArray'

How would I go about doing this in Java?

Thanks for any input - Phil

Your question must include a summary of the work you've done so far to solve the problem, and a description of the difficulty you are having solving it (help center, How to Ask). — Zabuzard
– Zabuzard, Commented Mar 11, 2019 at 20:59
If you can use TreeSet, its members are sorted and you can use your custom comparator to sort. — GaripTipici
– GaripTipici, Commented Mar 11, 2019 at 21:26

Harshit Sharma · Accepted Answer · 2019-03-11 21:05:27Z

1

Good and clean way to do is this:

// [[EHM, Evans, 45], [AB, Evans, 63]
List<List<String>> input = new ArrayList<>();
List<String> subInput;
subInput = new ArrayList<>();
subInput.add("EHM");
subInput.add("Evans");
subInput.add("45");
input.add(subInput);
subInput = new ArrayList<>();
subInput.add("AB");
subInput.add("Evans");
subInput.add("63");
input.add(subInput);

Collections.sort( input, (a,b) -> a.get(0).compareTo(b.get(0)) );
System.out.println(input);

answered Mar 11, 2019 at 21:05

Harshit Sharma

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1 Comment

Harshit Sharma Over a year ago

@venomphil please accept my answer if you think it helped answer your question

GaripTipici · Accepted Answer · 2019-03-11 21:39:19Z

0

You can use TreeSet of TreeSets.

TreeSet<TreeSet<String>> set = new TreeSet<>((s1, s2) -> s1.first().compareTo(s2.first()));
Set<String> subset1 = new TreeSet<>();
subset1.add("EHM");
subset1.add("Evans");
subset1.add("45");
Set<String> subset2 = new TreeSet<>();
subset2.add("AB");
subset2.add("Evans");
subset2.add("43");
set.add(subset1);
set.add(subset2);

TreeSets are sorted.

answered Mar 11, 2019 at 21:39

GaripTipici

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