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]]
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David Winsemius, MD
Alameda, CA, USA
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and provide commented, minimal, self-contained, reproducible code.
