[datatable-help] data.table BUG : data.table assignment

[Matthew Dowle]

By design. See ?":=" and ?copy.

If table1 is 20GB in RAM, you need to be explicit to tell data.table you
really really want to copy it; i.e., table2=copy(table1).

It deliberately breaks standard R practice. Which is partly why it's a new
operator that works differently.

http://stackoverflow.com/questions/10225098/understanding-exactly-when-a-data-table-is-a-reference-to-vs-a-copy-of-another


> Hello,
>
> see this example :
>
> require(data.table)
>
> table1<-data.table(id=c(1,2,3),x=c(1,2,3))
> table2<-table1
> table1[,y:=sum(x)]
> table1
> table2
>
> The problem ? Both of table1 and table2 have the variable 'y' BUT only
> table1 should.
>
> Thx
>
>
>
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