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From MSB <markbrd...@tiscali.co.uk>
Subject Re: Sorting by column(s)
Date Tue, 19 Jan 2010 07:49:29 GMT

I can only hazard a guess at which method would be 'better' (whatever that
means) but I do lean more towards the first option as it would require the
creation of fewer in memory objectsm reuse the existing worksheet and would
be cleaner - I can imagine the carnage created by a few faulty links.

Now, having said that, you should be fine writing new values into the
existing cells following the data sort, and it will not be necessary to
clear out the existing values in my opinion, simply call the setCellValue()
method and pass the 'new' value. The only caveat is that the data type
should be the same - i.e. write numbers into numeric cells etc - so that you
will not have the change the type of the existing worksheet cell. This could
be the one problem you will face as once the data has been written to the
csv file, you will lose all type information and everything will become a
String; it should be easy to overcome this however by 'remembering' the type
of the data in each column so that you can convert back before populating
the worksheet cells. Of course, the other advantage of this technique is
that you will retain any and all style information originally applied to the

It seems from your last post as if you are simply using POI to strip the
data from an existing Workbook, sort the data and then re-populate that same
workbook. I am forced to ask why? Would it not be far easier to simply use
Excel to open the file, perform the sort and then save the file back to disk
again? Of course, this assumes that you have access to Excel, that the file
does already exist and you are not creating it from scratch using POI.


Mark B

f.dcg wrote:
> Thx for the extensive reply.
> I have thought about using a collection but the effect on memory can be
> quite detrimental ..
> Esp since one never knows how big the files will be.
> So i had already started work on an alternate solution:
> - Export file to csv format
> - Do a *nix sort on it (fastest there is, afaik)
> - clear the workbook-sheet (or would overwriting the old entries be
> cheaper?)
> - Repopulate by means of file import and write the workbook back to disk
> (or
> just use it outright)
> OR (and this just popped into my head ;-) ) would the following be more
> efficient and faster:
> - Add a column to the sheet to be sorted that makes each row uniquely
> identifiable
> - Push the columns to be sorted on into a collection (incl the unique id
> column)
> - Sort the collection
> - Use the collection as a 'view' for the sheet or create a new sheet and
> fill it with links to the original rows (assuming this works?)
> * If the collection becomes to large one could do the csv export/ import
> thing as well (just with the required cols however.)
> I know the 1st solution will work, even with 50G files. But would the
> second
> solution be feasible as well, referring to the row links.
> Tia,
> Fermin DCG
> On Mon, Jan 18, 2010 at 5:40 PM, MSB <markbrdsly@tiscali.co.uk> wrote:
>> As far as I am aware, it is not possible to sort the data in columns
>> using
>> POI.
>> Have you considered using Java's support for collections to help you
>> overcome this problem - the Arrays.sort() method may be of some help and
>> if
>> not, it is always possible to create your own sorting algorithms. Then
>> all
>> you would need to do is write the data into one of the collections
>> classes,
>> sort that and then retrieve the data to populate the worksheet. Thinking
>> about this further, the JTable class may be the way to go; I know that it
>> is
>> possible to sort this on columns and I can see that it should be possible
>> to
>> create a JTable, populate it with data, sort the model and then retrieve
>> the
>> sorted data to populate the worksheet. Sadly, it has been a long time
>> since
>> I used Java to create GUIs and so I cannot remember all of the details
>> but
>> I
>> am confident it is possible, here is a good place to start
>> http://www.java2s.com/Tutorial/Java/0240__Swing/1100__JTable-Sort.htm.
>> You
>> may not even need to use the complex JTable object but can simply use the
>> model part of it's MCV design pattern, the
>> javax.swing.table.DefaultTableModel class.
>> Yours
>> Mark B
>> dcg wrote:
>> >
>> > Hi,
>> >
>> > How does one sort by one or more columns in POI?
>> >
>> > Undoubtfully this is a very basic (and simple?) question but for some
>> > reason
>> > i can't find any mention of it anywhere, nor am i able to locate a
>> method
>> > in
>> > the API the suggests column-sorting.
>> > I sincerely hope its due to the fact that i'm overlooking something
>> > bacause
>> > sorting a sheet seems quite basic.
>> >
>> > Any suggestions/ links as to how to sort columns would be much
>> > appreciated.
>> >
>> > Tia,
>> >
>> > Fermin DCG
>> >
>> >
>> --
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> -- 
> “The reasonable man adapts himself to the world; the unreasonable one
> persists in trying to adapt the world to himself. Therefore all progress
> depends on the unreasonable man.”
> - George Bernard Shaw (1856 - 1950)

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