Sorry David for this belate thank. Your code helped me so much. I tested a
class that does not inherit the data.frame class and it also worked. Maybe
I had problems with different kinds of method signatures of [ function.
For example, this does not work:
setMethod("[", signature(x="BigDataFrame", j="missing", drop="logical"),
function(x, i, drop=TRUE) {
exp <- substitute(i)
....
})
So my strategy now is dispatching on x only, defining a function with full
params and checking for missing(j) if needed:
setMethod("[", signature(x="myFrame"),
function(x,i,j,...,drop=TRUE) {
exp <- substitute(i)
if(!missing(j))
// do thing on j
....
})
Regards,
Nhan Vu
On Wed, May 15, 2013 at 10:24 AM, David Winsemius <dwinsem...@comcast.net>wrote:
>
> On May 14, 2013, at 8:02 PM, David Winsemius wrote:
>
> I think you need to read ?setClass and ?setMethod. There is an example of
>> defining a "[" method for a class that inherits from 'data.frame'. I
>> suspect you need to capture the various possibilities for the arguments
>> being present or missing.
>>
>>
> setClass("myFrame", contains = "data.frame",
> representation(callexp = "character"))
>
> df1 <- data.frame(x = 1:10, y = rnorm(10), z = sample(letters,10))
>
> mydf1 <- new("myFrame", df1, callexp = "")
>
> setMethod("[",
> signature(x = "myFrame"),
> function (x, i, j, ..., drop = TRUE)
> {callexp <- deparse(substitute(i))
> S3Part(x) <- callNextMethod()
> x@callexp <- callexp
> x
> }
> )
>
> mydf1[1:2, ]
> #--------------
> Object of class "myFrame"
> x y z
> 1 1 -1.9119574 f
> 2 2 0.2719548 i
> Slot "callexp":
> [1] "1:2"
>
> > mydf1[mydf1$x<5, ]
> Object of class "myFrame"
> x y z
> 1 1 -0.1065694 u
> 2 2 0.8571367 l
> 3 3 1.7259175 z
> 4 4 0.3618450 x
> Slot "callexp":
> [1] "mydf1$x < 5"
>
>
>
> --
>> David
>>
>> Sent from my iPhone
>>
>> On May 14, 2013, at 5:45 AM, Nhan Vu Lam Chi <nhani...@adatao.com> wrote:
>>
>> Dear David,
>>>
>>> First, I would like to say thank you for your very soon reply. Second, I
>>> want to clarify the question because it seems to not carrying exactly what
>>> I want to ask. Let take an example on R data.frame:
>>> V1 <- 1
>>> df2 <- df[V1== 1,] # df is a data.frame, this command is correct, right?
>>>
>>> The evaluation steps for the above command are:
>>> 1. R evaluate V1 > 1 to get TRUE
>>> 2. The command becomes df2 <- df[TRUE,] which copies all rows of df to
>>> df2
>>>
>>> What I want is to capture the "V1 > 1" expression instead of letting R
>>> do the evaluation in case of the custom [ function. Assume my class is
>>> mydf, the S4 function should be:
>>> setMethod("[", signature(x="mydf"), function(x,i,j,...,drop=TRUE) {
>>> e <- substitute(i)
>>> // do parsing and custom-evaluation tasks
>>> })
>>>
>>> Currently, i is always a vector of type character, numeric or logic due
>>> to R evaluation.
>>>
>>> I am a newbie to R, so please tolerate my mistakes or misunderstanding.
>>> Thanks!
>>> Nhan Vu
>>>
>>>
>>>
>>> On Tue, May 14, 2013 at 12:14 PM, David Winsemius <
>>> dwinsem...@comcast.net> wrote:
>>>
>>>>
>>>> On May 13, 2013, at 6:38 PM, Nhan Vu Lam Chi wrote:
>>>>
>>>> Hi everyone,
>>>>> I currently work on a S4 class that has the [ function. I want to
>>>>> capture
>>>>> the unevaluated expression corresponding to the i param using
>>>>> substitute()
>>>>> function and do a non-standard evaluation. However R automatically
>>>>> evaluates the expression and give me its value.
>>>>> For example:
>>>>> Given mydf[mydf$V1 > 1,] with mydf is an object of my custom S4
>>>>> dataframe
>>>>> class and V1 is one of its columns, I want to get the unevaluated
>>>>> expression mydf$V1 > 1.
>>>>>
>>>>> My questions are:
>>>>> 1. Is it possible to do that in R?
>>>>> 2. If yes, how to do?
>>>>>
>>>>
>>>> Doesn't this cry out for the S4 class definition of "[" to be
>>>> answerable?. Because "[" is generic, it could have almost any definition at
>>>> the whim of the package author.
>>>>
>>>> My R version and OS info are:
>>>>> R version 2.15.3 (2013-03-01) -- "Security Blanket"
>>>>> Copyright (C) 2013 The R Foundation for Statistical Computing
>>>>> ISBN 3-900051-07-0
>>>>> Platform: x86_64-pc-linux-gnu (64-bit)
>>>>>
>>>>> This is the first time I post to the mailing list, so please forgive
>>>>> any
>>>>> mistakes and/or advise me if possible.
>>>>> Regards,
>>>>> Nhan Vu
>>>>>
>>>>> [[alternative HTML version deleted]]
>>>>>
>>>>
>>>> You are forgiven, but this once, for posting in HTML.
>>>>
>>>> --
>>>> David Winsemius
>>>> Alameda, CA, USA
>>>>
>>>
>>>
>> [[alternative HTML version deleted]]
>>
>> ______________________________**________________
>> R-help@r-project.org mailing list
>> https://stat.ethz.ch/mailman/**listinfo/r-help<https://stat.ethz.ch/mailman/listinfo/r-help>
>> PLEASE do read the posting guide http://www.R-project.org/**
>> posting-guide.html <http://www.R-project.org/posting-guide.html>
>> and provide commented, minimal, self-contained, reproducible code.
>>
>
> David Winsemius, MD
> Alameda, CA, USA
>
>
[[alternative HTML version deleted]]
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