R help - Oct 2016 - strange output of cat function used in recursive function

2016-10-01 18:02 GMT+02:00 David Winsemius <dwinsemius at
comcast.net>:
>
>> On Oct 1, 2016, at 8:44 AM, Jan Kacaba <jan.kacaba at 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.

> On Oct 1, 2016, at 9:29 AM, Jan Kacaba <jan.kacaba at gmail.com>
wrote:
> 
> 2016-10-01 18:02 GMT+02:00 David Winsemius <dwinsemius at
comcast.net>:
>> 
>>> On Oct 1, 2016, at 8:44 AM, Jan Kacaba <jan.kacaba at
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.

-- 

David Winsemius
Alameda, CA, USA

> On Oct 1, 2016, at 9:39 AM, David Winsemius <dwinsemius at
comcast.net> wrote:
> 
> 
>> On Oct 1, 2016, at 9:29 AM, Jan Kacaba <jan.kacaba at gmail.com>
wrote:
>> 
>> 2016-10-01 18:02 GMT+02:00 David Winsemius <dwinsemius at
comcast.net>:
>>> 
>>>> On Oct 1, 2016, at 8:44 AM, Jan Kacaba <jan.kacaba at
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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David Winsemius
Alameda, CA, USA