And more info here (see both answers) :
http://stackoverflow.com/questions/10225098/understanding-exactly-when-a-data-table-is-a-reference-to-vs-a-copy-of-another
On 10/03/14 05:20, Michael Nelson wrote:
This is well explained in the help file for `copy` (and `setnames`)
DT <- DT2
does *not* create a copy, it creates two object names that refer to
the same object reference.
If you want force the creation of a copy, use `copy`
DT <- copy(DT2)
Then your example will work as expected.
------------------------------------------------------------------------
*From:* [email protected]
[[email protected]] on behalf of
Manabu Sakamoto [[email protected]]
*Sent:* Monday, 10 March 2014 4:00 PM
*To:* [email protected]
*Subject:* [datatable-help] setnames on copy data.table also renames
original data.table object
Dear list,
I have a data.table object for instance DT:
x <- seq(1:100)
y <- x^2
DT <- data.table(X=x, Y=y)
and I produce a copy
DT2 <- DT
which I rename
setnames(DT2, c("A","B"))
this somehow also renames DT, the names of which are now "A" and "B".
How can I just rename the copy and keep the names of the original?
Many thanks,
Manabu
--
Manabu Sakamoto, PhD
[email protected] <mailto:[email protected]>
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