[R] operator problem within function

Thu Apr 29 18:34:18 CEST 2010

That was copied from the help page the comes up with:

  ?"$"

It is rather "special".

--  
David.

On Apr 29, 2010, at 12:26 PM, Bunny, lautloscrew.com wrote:

> Nice, thx. Which manual do you use ? an introduction to R ? Or  
> something special ?
>
> matt
>
>
> On 29.04.2010, at 15:25, David Winsemius wrote:
>
>>
>> On Apr 29, 2010, at 9:03 AM, Bunny, lautloscrew.com wrote:
>>
>>> Sorry for that offlist post, did not mean to do it intentionally.  
>>> just hit the wrong button. Unfortunately this disadvantage is not  
>>> written next to $ in the manual.
>>
>> Hmmm. Not my manual:
>>
>> "Both [[ and $ select a single element of the list. The main  
>> difference is that $ does not allow computed indices, whereas  
>> [[does."
>>
>>
>> It also says that the correct equivalent using extraction operators  
>> of "$" would be:
>>
>> x$name  ==  x[["name", exact = FALSE]]
>> -- 
>> David.
>>>
>>>
>>>>
>>>> On Apr 29, 2010, at 2:34 AM, Bunny, lautloscrew.com wrote:
>>>>
>>>>> David,
>>>>>
>>>>> With your help i finally got it. THX!
>>>>> sorry for handing out some ugly names.
>>>>> Reason being: it´s a german dataset with german variable names.  
>>>>> With those german names you are always sure you dont use a  
>>>>> forbidden
>>>>> name. I just did not want to hit one of those by accident when  
>>>>> changing these names for the mailing list. columna is just the  
>>>>> latin term for column :) . Anyway here´s what worked
>>>>>
>>>>> note: I just tried to use some more "real" names here.
>>>>> 		
>>>>> recode_items = function(dataframe,question_number,medium=3){
>>>>> 		
>>>>> 		#note column names of the initial data.frame are like  
>>>>> Question1,Question2 etc. Using [,1] would not be very practical  
>>>>> since 		# the df contains some other data too. Indexing by names  
>>>>> seemed to most comfortable way so far.
>>>>> 		question<-paste("Question",question_number,sep="")
>>>>> 		# needed indexing here that understands characters, that´s why  
>>>>> going with [,question_number] did not work.
>>>>> 		dataframe[question][dataframe[question]==3]=0
>>>>
>>>> This would be more typical:
>>>>
>>>> dataframe[dataframe[question]==3, question] <- 0
>>>>
>>>>> 		
>>>>> 		
>>>>> 		return(dataframe)
>>>>> 	
>>>>> 	}
>>>>>
>>>>> recode_items(mydataframe,question_number,3)
>>>>> # this call uses the dataframe that contains the answers of  
>>>>> survey participants. Question number is an argument that selects  
>>>>> the question from the dataframe that should be recoded. In  
>>>>> surveys some weighting schemes only respect extreme answers,  
>>>>> which is why the medium answer is recoded to zero. Since it  
>>>>> depends on the item scale what medium actually is, I need it to  
>>>>> be an argument of my function.
>>>>>
>>>>>> Did you want a further logical test with that "=1" or some sort  
>>>>>> of assignment???
>>>>>
>>>>> So yes, it´s an assignment.
>>>>>
>>>>>>> Moral: Generally better to use "[" indexing.
>>>>>
>>>>> That´s what really made my day (and it´s only 9.30 a.m. here ) .  
>>>>> Are there exceptions to rule?
>>>>
>>>> Not that I know of.
>>>>
>>>>> I just worked a lot with the $ in the past.
>>>>
>>>> "$colname" is just syntactic sugar for either "["colname"]" or  
>>>> "[ ,"colname"]" and it has the disadvantage that colname is not  
>>>> evaluated.
>>>>
>>>>
>>>>>
>>>>> thx
>>>>>
>>>>> matt
>>>>>
>>>>> 	
>>>>>
>>>>>
>>>>> On 29.04.2010, at 00:56, David Winsemius wrote:
>>>>>
>>>>>>
>>>>>> On Apr 28, 2010, at 5:45 PM, David Winsemius wrote:
>>>>>>
>>>>>>>
>>>>>>> On Apr 28, 2010, at 5:31 PM, Bunny, lautloscrew.com wrote:
>>>>>>>
>>>>>>>> Dear all,
>>>>>>>>
>>>>>>>> i have a problem with processing dataframes within a function  
>>>>>>>> using the "$".
>>>>>>>> Here´s my code:
>>>>>>>>
>>>>>>>>
>>>>>>>> recode_items = function(dataframe,number,medium=2){
>>>>>>>> 	
>>>>>>>> 	# this works
>>>>>>>> 	q<-paste("columna",number,sep="")
>>>>>>>
>>>>>>> Do your really want q to equal "columna2" when "number" equals  
>>>>>>> 2?
>>>>>>>
>>>>>>>>
>>>>>>>> 	# this does not work, particularly because "dataframe" is  
>>>>>>>> not processed
>>>>>>>> 	# dataframe should be: givenframe$columnagivennumber
>>>>>>>> 	a=dataframe$q[dataframe$q==medium]=1
>>>>>>
>>>>>> Did you want a further logical test with that "=1" or some sort  
>>>>>> of assignment???
>>>>>>
>>>>>>>
>>>>>>> a) Do you want to work on the column from dataframe ( horrible  
>>>>>>> name for this purpose IMO) with the name "columna2"? If so,  
>>>>>>> then start with
>>>>>>>
>>>>>>> dataframe[ , q ]
>>>>>>>
>>>>>>> .... the "q" will be evaluated in this form whereas it would  
>>>>>>> not when used with "$".
>>>>>>>
>>>>>>> b) (A guess in absence of explanation of a goal.) Now do you  
>>>>>>> want all of the rows where that vector equals "medium"? If  
>>>>>>> so ,then try this:
>>>>>>>
>>>>>>> dataframe[ dataframe[ , q ]==2 , ]  # untested in the absence  
>>>>>>> of data
>>>>>>
>>>>>> Ooops. should have been:
>>>>>>
>>>>>> dataframe[ dataframe[ , q ]==medium , ] #since both q and  
>>>>>> medium will be evaluated.
>>>>>>
>>>>>>
>>>>>>>
>>>>>>> Moral: Generally better to use "[" indexing.
>>>>>>>
>>>>>>> -- 
>>>>>>> David.
>>>>>>>
>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> 	return(a)	
>>>>>>>>
>>>>>>>> }
>>>>>>>>
>>>>>>>>
>>>>>>>> If I call this function, i´d like it to return my   
>>>>>>>> dataframe.  The problem appears to be somewhere around the $.  
>>>>>>>> I´m sure this not too hard, but somehow i am stuck. I´ll keep  
>>>>>>>> searchin the manuals.
>>>>>>>> Thx for any help in advance.
>>>>>>>>
>>>>>>>> best
>>>>>>>>
>>>>>>>> matt
>>>>>>>> 	[[alternative HTML version deleted]]
>>>>>>>>
>>>>>>>> ______________________________________________
>>>>>>>> R-help at r-project.org mailing list
>>>>>>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>>>>>>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>>>>>>>> and provide commented, minimal, self-contained, reproducible  
>>>>>>>> code.
>>>>>>>
>>>>>>> ______________________________________________
>>>>>>> R-help at r-project.org mailing list
>>>>>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>>>>>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>>>>>>> and provide commented, minimal, self-contained, reproducible  
>>>>>>> code.
>>>>>>
>>>>>
>>>>
>>>
>>
>> David Winsemius, MD
>> West Hartford, CT
>>
>

David Winsemius, MD
West Hartford, CT