question related to ragged array

[ganesh pol]

friends i have problem related to ragged array
in ragged array
we create arrays of variable column length
eg

1
1 1
1 1 1
but how to create array which gives variable row length
1
1 1
1 1 1

[Nathaniel Stoddard]

int length = getLengthOfArray();
Object[] array = new Object[length];

[Ernest Friedman-Hill]

ganesh --

I don't think Mr. Stoddard is answering the question you asked, so I'll give it a try. Java "2D" arrays aren't really 2D, as you seem to know: a 2D array is a 1D array of column arrays. The number of columns is thus fixed, but the number of "rows" in each column can vary. You're asking, I think, if you can make an array with a fixed number of rows, but a different number of columns in each row. The answer, strictly, is no. But I can't think of a situation where this is really going to be a problem.

Is this just idle curiosity?

[ganesh pol]

bu suppaose if i have to really print some thing in which i have to change length of each row constant and keep changing column length can any one explain me it's code or give it in java

[Ernest Friedman-Hill]

I don't understand what you're getting at. In any case, just store the data the other way round: put your "rows" in the columns, and your "columns" in the rows.

[Kashif Iqbal Khan]

 
 
int[][] array = new int[3][]; // 2nd dimension is optional
array[0] = new int[1]; // first row has 1 columns
array[1] = new int[5]; // second row has 5 columns
array[2] = new int[10]; // third row has 10 columns
 

Alternatively

 
 
int[][] array = new int[3][]; // 2nd dimension is optional
for (int i=0 ; i< array.length ; i++)
        array[i] = new int[i*2]; 
 

[Ernest Friedman-Hill]

Mr. Khan,

Ummmm...

Note that I described a 2D array as being an array of columns. All you've done is to change the terms we're using; you're calling the columns "rows" and the rows "columns." You're certainly free to do that if you'd like -- that's what I was trying to say to Ganesh. But then you can no longer make an array with a fixed number of columns and a variable number of rows.

[KR Campbell]

If the structure of your arrays is truly important to you, perhaps the solution lies with linked lists? You could either have a LinkedList of LinkedList where each link in the list consists of another list or more simply an array of LinkedList. Then you can make it as 'ragged' as you like!

[KR Campbell]

... although thinking about it a bit more; it depends on whether it is acceptable to mimic a primitive data structure using an Object structure. I don't know. Obviously, you have to use method calls rather than assignment.

Also, it would be better to use a LinkedHashMap instead of a LinkedList as one of the key abilities of an array would seem to be its O(1) access time. This would give both relatively fast iterative and random access.

[Ilja Preuss]

Originally posted by KR Campbell:

Also, it would be better to use a LinkedHashMap instead of a LinkedList as one of the key abilities of an array would seem to be its O(1) access time. This would give both relatively fast iterative and random access.

An ArrayList would be better - it also gives you O(1) indexed access, without requiring you to manage the keys. In fact it is likely to be faster than a HashMap in absolute terms.

[KR Campbell]

Originally posted by Ilja Preuss:


An ArrayList would be better - it also gives you O(1) indexed access, without requiring you to manage the keys. In fact it is likely to be faster than a HashMap in absolute terms.

..Even better then ; but do you need to manage keys with the HashMap given that we are talking about integers? Can't you just wrap them in an Integer given that

 (new Integer(anyIntegerValue)).equals(new Integer(anyIntegerValue))  

?

[KR Campbell]

...sorry; I have to stop doing this post and then correct thing..

(new Integer(anyIntegerValue)).equals(new Integer(anyIntegerValue)) == true ;