Not sure if this is what your looking for, but to get one `data`-field of a large collection you can use `$collection->getColumnValues('attribute_code')`.

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__Edit:__

> How do you do when you want to know the data present in some object that you don't know what it contains ?

When talking about debugging large objects you can also use this. It will leave out any recursive data - so you'll get no blank screen or empty log file for large objects ...

    # if $item is some kind of Varien object
    Mage::log($item->debug());