I do not think of nested arrays in the same way as you do. You think encapsulation of arrays, whereas I thing 3 dimensional arrays. A cube for example, would serve you just fine. The first field would be the group, the second - the project, and the third (i'm guessing) the months. Using a hash is a better idea, because it allows instant access to the data once you know the keys. the code to parse through the following text HASH <xmp> __DATA__ GROUP1 PROJECT1 DECEMBER DATA GROUP2 PROJECT2 JANUARY DATA GROUP1 PROJECT6 JULY DATA GROUP4 PROJECT9 MAY DATA GROUP5 PROJECT5 AUGUST NOW __END DATA__ </xmp> is as follows:

while ( <DATA> ) {
    chomp( $_ );             #get rid of whitespace at end
    @f = split( /\s/, $_ );  #split data up into an array

    #ThreeDHash[ GROUP ][ PROJ  ][ MONTH ] = DATA
    $ThreeDHash{ $f[0] }{ $f[1] }{ $f[2] } = $f[ 4 ];
}
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For Arrays, you can put things into a 3d Array as follows

#same as a hash, only with square brackets 
# dont forget $index1/2/3 all have to be integers
# so you will have to index every entry to the file.
$ThreeDArray[ $index1 ][ $index2 ][ $index3 ] = $DATA;
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Have Fun. Regards, XDB19