Hello poopay, and welcome to the Monastery!

As explained in Excel::Writer::XLSX#DATES_AND_TIME_IN_EXCEL, Excel dates are stored internally as real numbers, but Spreadsheet::BasicRead and its relatives read dates in as strings. This means you have to manually extract the date from your input data, then convert it to a more convenient form. Here is one way to do this (adapted from the example given in the module documentation just referenced):

#! perl
use strict;
use warnings;
use Excel::Writer::XLSX;
use Spreadsheet::BasicRead;

my $workbook  = Excel::Writer::XLSX->new('perl.xlsx') or die "$!";
my $worksheet = $workbook->add_worksheet(); 
my @files     = ('data.xlsx');

foreach my $file (@files)
{
    my $excel = new Spreadsheet::BasicRead($file) or die "$!";
    my $row   = 0;

    while (my $dataref = $excel->getNextRow())
    {
        foreach my $date (@$dataref[7 .. 8])  # Columns H and I
        {
            $date =~ s[ ^ (\d{1,2}) / (\d{1,2}) / (\d{4}) $  ]
                      [ sprintf("%4d-%02d-%02d", $3, $2, $1) ]ex;
        }

        $worksheet->write_row($row++, 0, $dataref);
    }
}
[download]

Note: this approach will work only if you know the format(s) of the dates in your input files — or if you are prepared to expand the regex to allow for all the date formats you may encounter.

Update 1: I tested the above on an input file data.xlxs with Row 1 populated as follows:

1.1    2.1    3.3    4.4    5.5    6.6    7.7    9/15/2012    7/18/196
+0    8.8    9.9
[download]

The output file, perl.xlxs, had as Row 1:

1.1    2.1    3.3    4.4    5.5    6.6    7.7    2012-15-09    1960-18
+-07    8.8    9.9
[download]

as required.

Hope that helps,

Update 2: Why did you have a do {} block in your code snippet? As far as I can see, it serves no purpose there.

Thank you for the suggestion; I'll try this in a while. Will give feedback regarding the results. :)

Regarding the "do" block - I wasn't able to clean up the script before posting here. My bad. Will remove it in a while.

Hi Athanasius, I've tried the code but the output is still the same. Is it possible for me to send you the output file I was able to generate?

If I highlight the cell, it shows the formatting I want. But if I generate a pivot table from that, it will still cause me problems when I try to group the information.

The only solution for me at this time is to double-click each cell, then press "Enter" in order for the data to be displayed and treated correctly :(

Hello poopay,

I can think of only two ways to write formatted dates into an Excel spreadsheet using Excel::Writer::XLSX:

1. The ‘correct’ way is to convert the date string into Excel’s internal date format, namely a floating-point number. For example:

   use Excel::Writer::XLSX::Utility;
   ...
   my $ndate = xl_parse_date($date); 
   $worksheet->write_date_time($row, $col, $ndate, $format);
   [download]

   (Note that Excel::Writer::XLSX::Utility is installed along with Excel::Writer::XLSX, but its use may require the further installation of Date::Manip.)

   Unfortunately, application of the appropriate $format here leads to the problem you describe: the formatting is present, but is not applied to the date until the user double-clicks the cell and presses Enter. I don’t know why this is, and I haven’t found any way to make the formatting appear directly. Possibly a bug in Excel::Writer::XLSX?

2. Bypass Excel’s formatting by entering the date as a string. This is the method I suggested in my previous post. You say, “I’ve tried the code but the output is still the same.” Well, I don’t see how that’s possible, since a date written as a string is just a string, as far as Excel is concerned. The code I gave is a kludge, but it works correctly for me, as I showed.

Is it possible for me to send you the output file I was able to generate?

No, but I don’t see how that would help anyway. It would be much more useful for you to show the code you used, and just describe the resulting output.

...if I generate a pivot table...

According to the documentation, Excel::Writer::XLSX does not (yet) support the generation of pivot tables — this is mentioned in the TO DO section. So, how are you generating pivot tables?

Perhaps the best advice I can give is that you investigate alternative CPAN modules for writing Excel. :-(

Athanasius <°(((>< contra mundum