I wonder, how can I create a numeric zero-length vector in R?
If you read the help for vector (or numeric or logical or character or integer or double, 'raw' or complex etc ) then you will see that they all have a length (or length.out argument which defaults to 0
Therefore
numeric()
logical()
character()
integer()
double()
raw()
complex()
vector('numeric')
vector('character')
vector('integer')
vector('double')
vector('raw')
vector('complex')
All return 0 length vectors of the appropriate atomic modes.
# the following will also return objects with length 0
list()
expression()
vector('list')
vector('expression')
Simply:
x <- vector(mode="numeric", length=0)
Suppose you want to create a vector x whose length is zero. Now let v be any vector.
> v<-c(4,7,8)
> v
[1] 4 7 8
> x<-v[0]
> length(x)
[1] 0
This isn't a very beautiful answer, but it's what I use to create zero-length vectors:
0[-1] # numeric
""[-1] # character
TRUE[-1] # logical
0L[-1] # integer
A literal is a vector of length 1, and [-1] removes the first element (the only element in this case) from the vector, leaving a vector with zero elements.
As a bonus, if you want a single NA of the respective type:
0[NA] # numeric
""[NA] # character
TRUE[NA] # logical
0L[NA] # integer
来源：https://stackoverflow.com/questions/12614953/how-to-create-a-numeric-vector-of-zero-length-in-r