Simon Urbanek <simon.urba...@r-project.org> writes:
> On Oct 24, 2010, at 4:21 PM, Vitalie S. wrote:
>
>> David Winsemius <dwinsem...@comcast.net> writes:
>>
>>> On Oct 24, 2010, at 5:35 AM, Vitalie S. wrote:
>>>
>>>>
>>>> This might be just beyond of my understanding of how assignment works in
>>>> R, but
>>>> the documentation does not say anything about:
>>>>
>>>>> tv <- c(a="dsf", b="sss")
>>>>> tl <- list(232)
>>>>> `$<-`(tl, tv[[1]], "sdfdsfdsfsd")
>>>> Error: invalid subscript type 'language'
>>>
>>> Are either of these what you should have done to get what it appears you
>>> were aiming for but didn't specify?
>>>
>>
>> I meant what I wrote there. After the assignment, the list tl should have
>> element 'dsf' with the
>> value "sdfdsfdsfsd" (sorry for bad names).
>>
>
> No, as David pointed out the documentation tells you unmistakably:
> "[...] The main difference is that ‘$’ does not allow computed indices [...]"
> so you want to use `[[` instead since `$` is defined exactly to not allow
> just what you're doing: the index
> argument must be a symbol or a character vector of length one - anything else
> is an error as you see.
>
Oh, that was really stupid from my part. I meant that functionality for my
specific class, not for lists of course.
For list I would expect,
`$<-`(tl, tv[[1]], "sdfdsfdsfsd")
tl$`tv[[1]]` <- "sdfdsfdsfsd"
to give the same result.
I just gave this artificial example with lists to illustrate the error. Didn't
want to bring the definition of my classes here.
Vitalie.
> Cheers,
> Simon
>
>>> `$<-`(tl, "sdfdsfdsfsd", tv[[1]])
>>> # yields
>>> [[1]]
>>> [1] 232
>>>
>>> $sdfdsfdsfsd
>>> [1] "dsf"
>>>
>>>> `[<-`(tl, tv[[1]], "sdfdsfdsfsd")
>>> [[1]]
>>> [1] 232
>>>
>>> $dsf
>>> [1] "sdfdsfdsfsd"
>>>
>>> The "$" operator does not evaluate the index whereas the "[" function does.
>>> And the documentation is quite clear
>>> about that distinction.
>>>
>>
>> If it is evaluated or not it is hardly an explanation for the error. It
>> throws
>> the error before the method is even dispatched. If the index (in $'s case the
>> name) is unevaluated then my methods should get an expression 'tv[[1]]',
>> which I
>> can then handle.
>>
>> Example:
>>
>> setClass("classX", contains="list")
>> setMethod("$<-", "classX",
>> function(x, name, value){
>> print("I am here!!")
>> x
>> })
>>
>> x <- new("classX")
>> tv <- c("aa", "bb")
>> `$<-`(x, tv[[1]], 4343)
>> #gives
>> Error: invalid subscript type 'language'
>>
>>
>>> --
>>> David Winsemius.
>>>
>>>>
>>>> This happens even before the method is dispatched. I can not handle the
>>>> "name" argument in my S4 method, because it's not even entered.
>>>>
>>>> Thanks,
>>>> Vitalie.
>>
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>> https://stat.ethz.ch/mailman/listinfo/r-devel>
>>
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