> On Oct 1, 2016, at 9:39 AM, David Winsemius <dwinsem...@comcast.net> wrote:
>
>
>> On Oct 1, 2016, at 9:29 AM, Jan Kacaba <jan.kac...@gmail.com> wrote:
>>
>> 2016-10-01 18:02 GMT+02:00 David Winsemius <dwinsem...@comcast.net>:
>>>
>>>> On Oct 1, 2016, at 8:44 AM, Jan Kacaba <jan.kac...@gmail.com> wrote:
>>>>
>>>> Hello Dear R-help
>>>>
>>>> I tried to understand how recursive programming works in R. Bellow is
>>>> simple recursive function.
>>>>
>>>> binary1 <- function(n) {
>>>> if(n > 1) {
>>>> binary(as.integer(n/2))
>>>> }
>>>> cat(n %% 2)
>>>> }
>>>
>>> Did you mean to type "binary1(as.integer(n)"?
>>
>> Yes I meant that.
>>
>>>> When I call binary1(10) I get 1010. I believe that cat function stores
>>>> value to a buffer appending values as recursion proceeds and at the
>>>> end it prints the buffer. Am I right?
>>>
>>> No. Read the ?cat help page. It returns NULL. The material you see at the
>>> console is a side-effect.
>>>>
>>>> I tried to modify the function to get some understanding:
>>>>
>>>> binary2 <- function(n) {
>>>> if(n > 1) {
>>>> binary2(as.integer(n/2))
>>>> }
>>>> cat(n %% 2, sep=",")
>>>> }
>>>>
>>>> With call binary2(10) I get also 1010. Why the output is not separated
>>>> by commas?
>>>
>>> I think because there is nothing to separate when it prints (since there
>>> was no "buffer".
>>
>> If I use function:
>> binary3 <- function(n) {
>> if(n > 1) {
>> binary3(as.integer(n/2))
>> }
>> cat(n %% 2, ",")
>> }
>>
>> and call binary3(10) the console output is separated. So there must be
>> some kind of buffer and also it looks like there is some inconsistency
>> in how cat function behaves. Probably there is other explanation.
>
> The only inconsistency is how you sent arguments to cat. In the first
> instance you asked cat to display a single character value (and to separate
> multiple characters _if_present_ with a comma, .... but there were never any
> instances of a cat call with multiple arguments).
>
> In the second instance you told it to display single character values
> followed by a comma and it did that 4 times when the argument to the
> enclosing function was a decimal 10.
>
> If by buffer you mean the console stream, then I suppose I misunderstood your
> use of the term.
On the matter of a buffer, there is output buffering and a flush.console()
function. The only way I could get a regursive function to demonstrate a pause
between output with Sys.sleep was to instead use the Recall function:
?Recall
binary4 <- function(n) {
if(n > 1) {
Recall(as.integer(n/2))
}
cat(n %% 2, ","); flush.console(); Sys.sleep(2)
}
# halting 2 seconds between each appearance of a digit followed by a comma:
> binary4(10)
1 ,0 ,1 ,0 ,
>
> --
>
> David Winsemius
> Alameda, CA, USA
>
> ______________________________________________
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> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
David Winsemius
Alameda, CA, USA
______________________________________________
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