On Wed, 6 Jan 2010, Utkarsh Singhal wrote:
Hi All,
I ran the following lines in R:
print(object.size(a <- rep(1,10^6)),units="Mb")
print(object.size(a <- rep(3.542,10^6)),units="Mb")
print(object.size(b <- rep("x",10^6)),units="Mb")
print(object.size(b <- rep("xyzxyz xyz",10^6)),units="Mb")
print(object.size(b <- 1:10^6),units="Mb")
print(object.size(b <- rep(1:10,each=10^5)),units="Mb")
print(object.size(b <- rep(TRUE,10^6)),units="Mb")
The object size from first two lines is 7.6 MB, but from the last five it is
3.8 MB, although the length of vector is same.
Apparently, the size of any vector of a given length is twice if the vector
is numeric constant than if it is not.
Why is it so? Is my observation wrong? Or, is there some catch with
'object.size'?
Your observation is faulty. The first two are type "double", and a C
double takes 8 bytes. The last three are type "integer" or "logical"
with values stored in C int, 4 bytes each. Character strings are
harder to compute storage for as identical strings share storage. On
a 32-bit machine identical strings take an extra 4 bytes per string,
on a 64-bit machine an extra 8 bytes. If you look at the values in
bytes you will see that 'twice' is an approximation.
So
- the storage needed depends on the type of the vector as well as the
length.
- for character vectors it depends on the architecture and the
content.
Please do consult the R manuals rather than expect others to read them
for you: this is all in the 'R Internals' manual.
Thanks in advance.
Regards
Utkarsh
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