Hi all,
I've been trying to get a better handle on what manipulations lead R
to duplicate a vector, creating small experiments and using tracemem
to observe what happens (all in 2.15.1). That's lead me to a few
questions, illustrated using the snippet below.
x - 1:10
tracemem(x)
# [1]
Hadley Wickham hadley at rice.edu writes:
Why does x[5] - 5 create a copy
That assigns 5 not 5L. x is being coerced from integer to double.
x[5] - 5L doesn't copy.
, when x[11] (which should be
extending a vector does not) ? I can understand that maybe x[5] - 5
hasn't yet been optimised
Read the help carefully as to what 'copy' means:
When an object is traced any copying of the object by the C
function ‘duplicate’ produces a message to standard output, as
does type coercion and copying when passing arguments to ‘.C’ or
‘.Fortran’.
If you want to understand
Read the help carefully as to what 'copy' means:
When an object is traced any copying of the object by the C
function ‘duplicate’ produces a message to standard output, as
does type coercion and copying when passing arguments to ‘.C’ or
‘.Fortran’.
If you want to
On 12/07/2012 18:20, Hadley Wickham wrote:
Read the help carefully as to what 'copy' means:
When an object is traced any copying of the object by the C
function ‘duplicate’ produces a message to standard output, as
does type coercion and copying when passing arguments to ‘.C’
But does this?
z - as.list(x)
z$a - 11
Yes of course, as z is now of length 11. There is no provision in R to
extend a vector except by creating a new one. (Well, there is at C level
but I think it is not currently used.)
I guess a better example is
z - list(a = 1:1e6, b = runif(1e6))
The list gets copied, but do a and b, or does the new list point to
the existing locations? The following test suggests that it's a deep
copy.
x - 1:1e7
z - list(a = x)
system.time(replicate(100, z$b - 1L)) / 100
# ~ 0.05s
system.time(replicate(100, x[1e6 + 1L] - 1L)) / 100
# ~ 0.04s
Hi all,
In my continued effort to understand when and what R copies, I've
designed a small experiment to try and figure out what goes on when a
list gets copied - is it a shallow copy or a deep copy. I believe the
following experiment isolates the difference:
options(digits = 2)
powers - 4:6
n -
