How to create a numeric vector of zero length 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)