R help - Aug 2012 - How to modify the values of the parameters passing via ...

Dear Friends,

Let's assume there are three parameters that were passed into fun1. In
fun1, we need to modify one para but the remains need to be untouched. And
then all parameters were passed into fun2. However, I have failed to
achieve it.

Please see the following code.

##########################################
fun1 <-function(x, y, z=10) {x+y+z;}

fun2 <-function(aa, ...) {
  a=fun1(x=aa, y=5);    # works well  a=1+5+10=16
  b=fun1(x=aa, ...);       # works well  b=1+4+8=13
  y=0                          # it will not affect values passed using ...
  c=fun1(x=aa, ...)        # works well but c = 1+4+8=13

#   Some time we may only want to use parts of the inputed variables
#   we only want to modify y
  d=fun1(x=aa, y=5, ...);  #error : formal argument "y" matched by
multiple
actual arguments
#How can I get the result   d=1+5+8=14?

  c(a, b, c)
}

fun2(x=1, y=4, z=8)
##########################################

I will appreciate it if you would give me any suggestions.

Best wishes,

Zhiqiu

	[[alternative HTML version deleted]]

Hello,

You could see what is fun1 receiving with this modification meant for 
debugging:

fun1 <-function(x, y, z=10){
     print(match.call())
     x + y + z
}

Anyway, there is s standard way of dealing with argument '...' when one 
needs to know what was passed.
Include dots <- list(...) at the beginning of fun2 and then use it when 
necessary:

fun1 <-function(x, y, z=10){x + y + z}

fun2 <-function(aa, ...) {
   dots <- list(...)
   a <- fun1(x=aa, y=5)    # works well  a=1+5+10=16
   b <- fun1(x=aa, ...)    # works well  b=1+4+8=13
   y <- 0                  # it will not affect values passed using ...
   c <- fun1(x=aa, ...)    # works well but c = 1+4+8=13
   d <- fun1(x=aa, y=5, dots$z)  # works well  d=1+5+8=14
   c(a, b, c, d)
}

fun2(aa=1, y=4, z=8)
[1] 16 13 13 14


Also, to end statements with ';' is a C language tique, R doesn't
need it.
(Nor it hurts.)

Hope this helps,

Rui Barradas

Em 30-08-2012 23:07, Zhiqiu Hu escreveu:
> Dear Friends,
>
> Let's assume there are three parameters that were passed into fun1. In
> fun1, we need to modify one para but the remains need to be untouched. And
> then all parameters were passed into fun2. However, I have failed to
> achieve it.
>
> Please see the following code.
>
> ##########################################
> fun1 <-function(x, y, z=10) {x+y+z;}
>
> fun2 <-function(aa, ...) {
>    a=fun1(x=aa, y=5);    # works well  a=1+5+10=16
>    b=fun1(x=aa, ...);       # works well  b=1+4+8=13
>    y=0                          # it will not affect values passed using
...
>    c=fun1(x=aa, ...)        # works well but c = 1+4+8=13
>
> #   Some time we may only want to use parts of the inputed variables
> #   we only want to modify y
>    d=fun1(x=aa, y=5, ...);  #error : formal argument "y" matched
by multiple
> actual arguments
> #How can I get the result   d=1+5+8=14?
>
>    c(a, b, c)
> }
>
> fun2(x=1, y=4, z=8)
> ##########################################
>
> I will appreciate it if you would give me any suggestions.
>
> Best wishes,
>
> Zhiqiu
>
> 	[[alternative HTML version deleted]]
>
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