[R] [FORGED] custom function gives unexpected result - for me

[Rolf Turner]

The answer is very simple:  parentheses.  (Also think about "operator 
precedence".) If you assign rn <- 3, then 1:rn-1 is:

[1] 0 1 2

The "-" operator is applied *after*  the ":" operator.

You want 1:(rn-1) which gives

[1] 1 2

and the desired result.

cheers,

Rolf Turner

On 18/04/20 7:55 am, Monica Palaseanu-Lovejoy wrote:
> Hi,
> 
> I wrote a relatively simple function. If i run the code inside the function
> line by line i am getting the result i was expecting, but if i run the
> function, i get a different result.
> 
> The function:
> 
> grr1 <- function(rn) {
> r.up <- c()
> for (i in 1:rn-1) {
> if (i%%2==0) ru <- seq(1,i) else ru <- seq(i,1)
> r.up <- c(r.up, ru)
> }
> return(r.up)
> }
> 
> So, if rn is 3 for example i would expect to get 1 1 2
> 
> grr1(3)
> [1] 1 0 1 1 2
> 
> If i run it line by line inside the function:
> r.up <- c()
>> r.up
> NULL
> 
> i=1
> if (i%%2==0) ru <- seq(1,i) else ru <- seq(i,1)
>> ru
> [1] 1
> 
> r.up <- c(r.up, ru)
> r.up
> [1] 1
> 
> i=2
> if (i%%2==0) ru <- seq(1,i) else ru <- seq(i,1)
> ru
> [1] 1 2
> r.up <- c(r.up, ru)
>> r.up
> [1] 1 1 2
> 
> So - i am getting the result i am expecting. From where the 1 0 before what
> i expect as a result comes from? I am sure i am doing some very basic
> error, but it seems i cannot figure it out.
> 
> I run R x64  3.2.6. I know it is not the latest version, but it should not
> give me unexpected results because of that i would think.
> 
> sessionInfo()
> R version 3.6.2 (2019-12-12)
> Platform: x86_64-w64-mingw32/x64 (64-bit)
> Running under: Windows 10 x64 (build 17763)
> 
> Matrix products: default
> 
> locale:
> [1] LC_COLLATE=English_United States.1252
> [2] LC_CTYPE=English_United States.1252
> [3] LC_MONETARY=English_United States.1252
> [4] LC_NUMERIC=C
> [5] LC_TIME=English_United States.1252
> 
> attached base packages:
> [1] stats     graphics  grDevices utils     datasets  methods   base
> 
> loaded via a namespace (and not attached):
> [1] compiler_3.6.2
> 
> Thanks,
> Monica