[R] documentation of intersect() on string vector and num vector and on duplicated elements

[David Winsemius]

On Dec 2, 2009, at 5:00 PM, Peng Yu wrote:

> On Wed, Dec 2, 2009 at 3:51 PM, David Winsemius <dwinsemius at comcast.net 
> > wrote:
>> On Dec 2, 2009, at 4:33 PM, Peng Yu wrote:
>>
>>>> intersect(c(1,3,2),c('1','3'))   # note x is numeric and y is  
>>>> character
>>>
>>> [1] "1" "3"
>>>
>>> Apparently, intersect() treats num as string. But this is not
>>> documented in the help. Could somebody add it in the future  
>>> version of
>>> R?
>>
>> It is documented that intersect will return a value of that is same  
>> mode as
>> its "y" argument. How could it be any more clear?
>>
>>>
>>> Also according to the help, the argument should not have duplicated
>>> elements.
>>
>> That's not what my help page says. It says that "conceptually" they  
>> won't
>> have them, but immediately thereafter it says:
>> "Details
>> Each of union, intersect, setdiff and setequal will discard any  
>> duplicated
>> values in the arguments, and they apply as.vector to their  
>> arguments (and so
>> in particular coerce factors to character vectors)."
>>
>> Unfortunately, R does not have a package that will ensure that  
>> users will
>> read the help pages carefully.
>
> I didn't read Details.

If you are not going to read the help page, then please stop asking  
for corrections to it.

> Because I was interested in the arguments. The
> problem of some R document is that some information should gathered
> together are spread into multiple places. In particular, in the help
> of intersect, the first line of 'Details' should be merged with
> 'Argument' to make the help page clear and easy to read.
>
>> --
>>
>> David
>>
>>> But I tried the following example, it seems that it doesn't
>>> matter where there are duplicated elements or not. Should the help  
>>> be
>>> corrected? Or somebody could provide me with an example that make
>>> intersect() fails if there are duplicated elements?
>>>
>>>> x=c(3,1,2,1,7)
>>>> y=c(5,1,4,2,3,8,1)
>>>> x
>>>
>>> [1] 3 1 2 1 7
>>>>
>>>> y
>>>
>>> [1] 5 1 4 2 3 8 1
>>>>
>>>> intersect(x,y)
>>>
>>> [1] 3 1 2
>


David Winsemius, MD
Heritage Laboratories
West Hartford, CT