How to transform a regular array into two dimensional jagged array?

Question

I have a String array

String myArray [] = {"user1", "doc2", "doc5", "user2", "doc3", "doc6", "doc8", "user3", "doc 10" }

The meaning is that user1 has doc2 and doc5 ... user3 has only doc10 etc

I want to transform this array into a two dimensional jagged

String myArray2 [] [] = { {"user1", "doc2", "doc5"} , {"user2", "doc3", "doc6", "doc8"} , {"user3", "doc 10"} }

How can I do this most effectively? ( I have a logic that works by encountering an element that has a substring "user" and creating a new element of the jagged array. But I am sure my algorithm is far from the most efficient one)

most effectively? Create a User object with a Collection<String>/Collection<Doc> of documents. — Josh M
– Josh M, Commented Nov 18, 2013 at 0:27
I thought that there is something like split that could also be applied not only to a string but also to an array, splitting it into the next level array — Aleksei Nikolaevich
– Aleksei Nikolaevich, Commented Nov 18, 2013 at 0:28
Not that I know of. It'd be much better to maintain a Collection<User> of users instead of an array of arrays. — Josh M
– Josh M, Commented Nov 18, 2013 at 0:30

Jason C · Accepted Answer · 2013-11-18 00:39:59Z

A few things:

First, it sounds like you already have an algorithm that works. What is the problem? In cases like this there is no "most effective". There is only effective (it produces correct results), and not effective (it produces incorrect results). You have created an algorithm that satisfies your requirements. You are done.

Second, what do you mean by "most efficient"? Are your specific performance requirements not being met? If not, profile, identify the bottleneck, and optimize there. Is this part of the code slowing down your software to the point that an improvement would be noticeable? If not, your performance requirements are satisfied, and you are done.

Or, by "most efficient", do you mean "less lines of code"? Why? Is your code clear? Is it easy to maintain and can a reader easily see what its intentions are? If not, consider adding descriptive comments. If so, then you have nothing to gain and you are done.

If your algorithm is not behaving as intended, then you may post your specific problem, as well as how your actual and expected outputs differ. However, it sounds like you don't have any problems at all here. I recommend moving on to the next development task.

All that said, the way you are doing it is reasonable. Your task is essentially parsing tokens. Go through the array, find user strings, associate following values with that user, store data. There isn't much more you can do.

Sergey Kalinichenko · Accepted Answer · 2013-11-18 00:31:04Z

1

There is very little that you can do to make it efficient: you do need to create all the arrays that go into the jagged array, and you also need to do all the copying. There are no opportunities for saving much CPU time here.

You can avoid resizing arrays by first counting how many array elements the result is going to have, creating the result array, and then scan the array from the beginning again for the next position of "userX", and calling arrayCopy to copy the elements into the sub-arrays of the output array.

answered Nov 18, 2013 at 0:31

Sergey Kalinichenko

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