NVL: Convenience functions for handling 'NULL' objects.

In statnet.common: Common R Scripts and Utilities Used by the Statnet Project Software

Convenience functions for handling NULL objects.

Description

Convenience functions for handling NULL objects.

Usage

NVL(...)

NVL2(test, notnull, null = NULL)

NVL3(test, notnull, null = NULL)

EVL(...)

EVL2(test, notnull, null = NULL)

EVL3(test, notnull, null = NULL)

NVL(x) <- value

EVL(x) <- value

Arguments

..., test	expressions to be tested.
notnull	expression to be returned if test is not NULL.
null	expression to be returned if test is NULL.
x	an object to be overwritten if NULL.
value	new value for x.

Functions

• NVL(): Inspired by SQL function NVL, returns the first argument that is not NULL, or NULL if all arguments are NULL.

• NVL2(): Inspired by Oracle SQL function NVL2, returns the second argument if the first argument is not NULL and the third argument if the first argument is NULL. The third argument defaults to NULL, so NVL2(a, b) can serve as shorthand for (if(!is.null(a)) b).

• NVL3(): Inspired by Oracle SQL NVL2 function and magittr %>% operator, behaves as NVL2 but .s in the second argument are substituted with the first argument.

• EVL(): As NVL, but for any objects of length 0 (Empty) rather than just NULL. Note that if no non-zero-length arguments are given, NULL is returned.

• EVL2(): As NVL2, but for any objects of length 0 (Empty) rather than just NULL.

• EVL3(): As NVL3, but for any objects of length 0 (Empty) rather than just NULL.

• NVL(x) <- value: Assigning to NVL overwrites its first argument if that argument is NULL. Note that it will always return the right-hand-side of the assignment (value), regardless of what x is.

• EVL(x) <- value: As assignment to NVL, but for any objects of length 0 (Empty) rather than just NULL.

Note

Whenever possible, these functions use lazy evaluation, so, for example NVL(1, stop("Error!")) will never evaluate the stop call and will not produce an error, whereas NVL(NULL, stop("Error!")) would.

See Also

NULL, is.null, if

Examples

a <- NULL

a # NULL
NVL(a,0) # 0

b <- 1

b # 1
NVL(b,0) # 1

# Here, object x does not exist, but since b is not NULL, x is
# never evaluated, so the statement finishes.
NVL(b,x) # 1

# Also,
NVL(NULL,1,0) # 1
NVL(NULL,0,1) # 0
NVL(NULL,NULL,0) # 0
NVL(NULL,NULL,NULL) # NULL

NVL2(a, "not null!", "null!") # "null!"
NVL2(b, "not null!", "null!") # "not null!"

NVL3(a, "not null!", "null!") # "null!"
NVL3(b, .+1, "null!") # 2

NVL(NULL*2, 1) # numeric(0) is not NULL
EVL(NULL*2, 1) # 1


NVL(a) <- 2
a # 2
NVL(b) <- 2
b # still 1

statnet.common documentation built on Oct. 6, 2024, 5:06 p.m.