Just caught up with this thread.
is it allowed usage of having names for column vectors?
It wasn't intended, no. It would slow down grouping if it had to
maintain the names attribute too in the subsets. data.table is
intended to be used as a list of plain columns and the internals assume
that. names(DT$col) might exist though if data.table() has used a
reference to an input without taking a copy. It would then copy on
first := to that column and drop the names attribute at that point.
Which is why we might like to leave names there and just not use them.
But I'm thinking data.table() should drop names then to make this
cleaner. Despite that meaning a copy of the vector has to be taken if
it has names. A copy is taken currently anyway. But in GNU R 3.1.0,
with list() no longer copying named inputs, we can do more on that front.
Matthew
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