What is the logic of this function in R?
I'm studying about arguments in R functions, but I have some problem to understand the logic of it.
h <- function(a = 1, b = d){
d <- (a + 1)^2
c(a, b)
}
h()
# [1] 1 4
I expected the error message would be return because there is no value of b.
d is created under h function but there is no code like b = d which assign a value to b in function h .
However, the result is [1] 1 4.
How were b and d linked?
r function variable-assignment
edited Feb 7 at 14:11
chrki
4,77242547
asked Feb 7 at 8:04
Song LeeSong Lee
964
add a comment |
I'm studying about arguments in R functions, but I have some problem to understand the logic of it.
h <- function(a = 1, b = d){
d <- (a + 1)^2
c(a, b)
}
h()
# [1] 1 4
I expected the error message would be return because there is no value of b.
d is created under h function but there is no code like b = d which assign a value to b in function h .
However, the result is [1] 1 4.
How were b and d linked?
r function variable-assignment
edited Feb 7 at 14:11
chrki
4,77242547
asked Feb 7 at 8:04
Song LeeSong Lee
964
add a comment |
I'm studying about arguments in R functions, but I have some problem to understand the logic of it.
h <- function(a = 1, b = d){
d <- (a + 1)^2
c(a, b)
}
h()
# [1] 1 4
I expected the error message would be return because there is no value of b.
d is created under h function but there is no code like b = d which assign a value to b in function h .
However, the result is [1] 1 4.
How were b and d linked?
r function variable-assignment
edited Feb 7 at 14:11
chrki
4,77242547
asked Feb 7 at 8:04
Song LeeSong Lee
964
I'm studying about arguments in R functions, but I have some problem to understand the logic of it.
h <- function(a = 1, b = d){
d <- (a + 1)^2
c(a, b)
}
h()
# [1] 1 4
I expected the error message would be return because there is no value of b.
d is created under h function but there is no code like b = d which assign a value to b in function h .
However, the result is [1] 1 4.
How were b and d linked?
r function variable-assignment
r function variable-assignment
edited Feb 7 at 14:11
chrki
4,77242547
asked Feb 7 at 8:04
Song LeeSong Lee
964
edited Feb 7 at 14:11
chrki
4,77242547
asked Feb 7 at 8:04
Song LeeSong Lee
964
edited Feb 7 at 14:11
chrki
4,77242547
edited Feb 7 at 14:11
chrki
4,77242547
edited Feb 7 at 14:11
chrki
4,77242547
4,77242547
asked Feb 7 at 8:04
Song LeeSong Lee
964
asked Feb 7 at 8:04
Song LeeSong Lee
964
asked Feb 7 at 8:04
Song LeeSong Lee
964
964
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
Default function arguments values are lazily evaluated in R (i.e. evaluated only when they're needed):
See the output of this code for an example :
printme <- function(name,x){cat('evaluating',name,'n');x}
h <- function(a = printme('a',1), b = printme('b',d)){
cat('computing d...n')
d <- (a + 1)^2
cat('d computedn')
cat('concatenating a and b...n')
c(a, b)
cat('a and b concatenatedn')
}
h()
Console output :
computing d...
evaluating a
d computed
concatenating a and b...
evaluating b
a and b concatenated
As you can see, d is calculated before evaluating the default value of b
EDIT :
Furthermore, as correctly pointed out by @BrodieG in the comments, default arguments are evaluated in the function environment; in fact, in the example above, b can be initialized to the value of variable d that is defined inside the function environment.
Instead, when you specify a argument (without using the default), the expression that assigns the parameter is still lazily evaluated, but this time in the calling environment e.g. :
# same functions as above, but this time we specify the parameters in the call
h(a=printme('a',123),b=printme('d',d))
Console output :
computing d...
evaluating a
d computed
concatenating a and b...
evaluating d
Error in printme("d", d) : object 'd' not found
Note the error when argument b is evaluated because d cannot be found in the calling environment.
answered Feb 7 at 8:17
digEmAlldigEmAll
47.3k990125
2
Might be worth highlighting that default arguments are evaluated in the environment of the function they belong to, not in the calling environment like non-default arguments.
– BrodieG
Feb 7 at 13:18
@BrodieG: good idea, edited my answer ;)
– digEmAll
Feb 7 at 18:28
add a comment |
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1 Answer
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active
oldest
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1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
Default function arguments values are lazily evaluated in R (i.e. evaluated only when they're needed):
See the output of this code for an example :
printme <- function(name,x){cat('evaluating',name,'n');x}
h <- function(a = printme('a',1), b = printme('b',d)){
cat('computing d...n')
d <- (a + 1)^2
cat('d computedn')
cat('concatenating a and b...n')
c(a, b)
cat('a and b concatenatedn')
}
h()
Console output :
computing d...
evaluating a
d computed
concatenating a and b...
evaluating b
a and b concatenated
As you can see, d is calculated before evaluating the default value of b
EDIT :
Furthermore, as correctly pointed out by @BrodieG in the comments, default arguments are evaluated in the function environment; in fact, in the example above, b can be initialized to the value of variable d that is defined inside the function environment.
Instead, when you specify a argument (without using the default), the expression that assigns the parameter is still lazily evaluated, but this time in the calling environment e.g. :
# same functions as above, but this time we specify the parameters in the call
h(a=printme('a',123),b=printme('d',d))
Console output :
computing d...
evaluating a
d computed
concatenating a and b...
evaluating d
Error in printme("d", d) : object 'd' not found
Note the error when argument b is evaluated because d cannot be found in the calling environment.
answered Feb 7 at 8:17
digEmAlldigEmAll
47.3k990125
2
Might be worth highlighting that default arguments are evaluated in the environment of the function they belong to, not in the calling environment like non-default arguments.
– BrodieG
Feb 7 at 13:18
@BrodieG: good idea, edited my answer ;)
– digEmAll
Feb 7 at 18:28
add a comment |
Default function arguments values are lazily evaluated in R (i.e. evaluated only when they're needed):
See the output of this code for an example :
printme <- function(name,x){cat('evaluating',name,'n');x}
h <- function(a = printme('a',1), b = printme('b',d)){
cat('computing d...n')
d <- (a + 1)^2
cat('d computedn')
cat('concatenating a and b...n')
c(a, b)
cat('a and b concatenatedn')
}
h()
Console output :
computing d...
evaluating a
d computed
concatenating a and b...
evaluating b
a and b concatenated
As you can see, d is calculated before evaluating the default value of b
EDIT :
Furthermore, as correctly pointed out by @BrodieG in the comments, default arguments are evaluated in the function environment; in fact, in the example above, b can be initialized to the value of variable d that is defined inside the function environment.
Instead, when you specify a argument (without using the default), the expression that assigns the parameter is still lazily evaluated, but this time in the calling environment e.g. :
# same functions as above, but this time we specify the parameters in the call
h(a=printme('a',123),b=printme('d',d))
Console output :
computing d...
evaluating a
d computed
concatenating a and b...
evaluating d
Error in printme("d", d) : object 'd' not found
Note the error when argument b is evaluated because d cannot be found in the calling environment.
answered Feb 7 at 8:17
digEmAlldigEmAll
47.3k990125
2
Might be worth highlighting that default arguments are evaluated in the environment of the function they belong to, not in the calling environment like non-default arguments.
– BrodieG
Feb 7 at 13:18
@BrodieG: good idea, edited my answer ;)
– digEmAll
Feb 7 at 18:28
add a comment |
Default function arguments values are lazily evaluated in R (i.e. evaluated only when they're needed):
See the output of this code for an example :
printme <- function(name,x){cat('evaluating',name,'n');x}
h <- function(a = printme('a',1), b = printme('b',d)){
cat('computing d...n')
d <- (a + 1)^2
cat('d computedn')
cat('concatenating a and b...n')
c(a, b)
cat('a and b concatenatedn')
}
h()
Console output :
computing d...
evaluating a
d computed
concatenating a and b...
evaluating b
a and b concatenated
As you can see, d is calculated before evaluating the default value of b
EDIT :
Furthermore, as correctly pointed out by @BrodieG in the comments, default arguments are evaluated in the function environment; in fact, in the example above, b can be initialized to the value of variable d that is defined inside the function environment.
Instead, when you specify a argument (without using the default), the expression that assigns the parameter is still lazily evaluated, but this time in the calling environment e.g. :
# same functions as above, but this time we specify the parameters in the call
h(a=printme('a',123),b=printme('d',d))
Console output :
computing d...
evaluating a
d computed
concatenating a and b...
evaluating d
Error in printme("d", d) : object 'd' not found
Note the error when argument b is evaluated because d cannot be found in the calling environment.
answered Feb 7 at 8:17
digEmAlldigEmAll
47.3k990125
Default function arguments values are lazily evaluated in R (i.e. evaluated only when they're needed):
See the output of this code for an example :
printme <- function(name,x){cat('evaluating',name,'n');x}
h <- function(a = printme('a',1), b = printme('b',d)){
cat('computing d...n')
d <- (a + 1)^2
cat('d computedn')
cat('concatenating a and b...n')
c(a, b)
cat('a and b concatenatedn')
}
h()
Console output :
computing d...
evaluating a
d computed
concatenating a and b...
evaluating b
a and b concatenated
As you can see, d is calculated before evaluating the default value of b
EDIT :
Furthermore, as correctly pointed out by @BrodieG in the comments, default arguments are evaluated in the function environment; in fact, in the example above, b can be initialized to the value of variable d that is defined inside the function environment.
Instead, when you specify a argument (without using the default), the expression that assigns the parameter is still lazily evaluated, but this time in the calling environment e.g. :
# same functions as above, but this time we specify the parameters in the call
h(a=printme('a',123),b=printme('d',d))
Console output :
computing d...
evaluating a
d computed
concatenating a and b...
evaluating d
Error in printme("d", d) : object 'd' not found
Note the error when argument b is evaluated because d cannot be found in the calling environment.
answered Feb 7 at 8:17
digEmAlldigEmAll
47.3k990125
edited Feb 7 at 18:27
answered Feb 7 at 8:17
digEmAlldigEmAll
47.3k990125
answered Feb 7 at 8:17
digEmAlldigEmAll
47.3k990125
answered Feb 7 at 8:17
digEmAlldigEmAll
47.3k990125
47.3k990125
2
Might be worth highlighting that default arguments are evaluated in the environment of the function they belong to, not in the calling environment like non-default arguments.
– BrodieG
Feb 7 at 13:18
@BrodieG: good idea, edited my answer ;)
– digEmAll
Feb 7 at 18:28
add a comment |
2
Might be worth highlighting that default arguments are evaluated in the environment of the function they belong to, not in the calling environment like non-default arguments.
– BrodieG
Feb 7 at 13:18
@BrodieG: good idea, edited my answer ;)
– digEmAll
Feb 7 at 18:28
2
2
Might be worth highlighting that default arguments are evaluated in the environment of the function they belong to, not in the calling environment like non-default arguments.
– BrodieG
Feb 7 at 13:18
Might be worth highlighting that default arguments are evaluated in the environment of the function they belong to, not in the calling environment like non-default arguments.
– BrodieG
Feb 7 at 13:18
@BrodieG: good idea, edited my answer ;)
– digEmAll
Feb 7 at 18:28
@BrodieG: good idea, edited my answer ;)
– digEmAll
Feb 7 at 18:28
add a comment |
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