Well the problem with pack comes from using 'nan' and 'inf' there. Now basicly with pure numbers, i could:

# packing
$str=pack ("d*",@numbers);
# unpacking to a correct column
$val=(unpack("d*",$str))[$col];
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But that wont work if there is 'nan' in the @numbers array, will it?

I quess i could save memory by use pack in read loop. Thus pushing the limit back to a point. But i have to think that splitting.