[R] Fwd: Conditional inclusion of an element in an R object

[Bert Gunter]

Don's response seems apropos to me. Do you understanding indexing,
i.e. the "[" operator? If not, you should read An Introduction to R or
other tutorial (there are many good ones on the web). If that is not
the issue, you need to explain more clearly why his answer does not
suffice.

Cheers,
Bert

Bert Gunter
Genentech Nonclinical Biostatistics
(650) 467-7374

"Data is not information. Information is not knowledge. And knowledge
is certainly not wisdom."
H. Gilbert Welch




On Fri, Jan 10, 2014 at 1:59 PM, Santosh <santosh2005 at gmail.com> wrote:
> My intention is to include certain columns if they meet certain criteria.
> For example, if "b" is one of the columns of a1, then keep otherwise don't.
>
> HTH..
> santosh
>
>
> On Fri, Jan 10, 2014 at 1:01 PM, MacQueen, Don <macqueen1 at llnl.gov> wrote:
>
>> Apologies, but all that ifelse() stuff is too hard to follow.
>>
>> What I would do is compute a character vector of column names to keep,
>> then do
>>
>>   a1[ , names.to.keep]
>>
>> -Don
>>
>> --
>> Don MacQueen
>>
>> Lawrence Livermore National Laboratory
>> 7000 East Ave., L-627
>> Livermore, CA 94550
>> 925-423-1062
>>
>>
>>
>>
>>
>> On 1/10/14 12:53 PM, "Santosh" <santosh2005 at gmail.com> wrote:
>>
>> >Dear Rxperts...
>> >
>> >I would like to conditionally include an element (as a column) in a
>> >dataframe. Please see the  sample code below:
>> >
>> >There is a correction to the earlier post.. my apologies...
>> >a1 <- data.frame(P=rep(1,10),Qr=LETTERS[1:10],b=letters[1:10],
>> >R=rep(c("A","B"),each=5))
>> >
>> > lc1 <- list(C1 = "P",C2 =
>> >ifelse(is.element("Q",names(a1)),"Q",ifelse(is.element("b",names(a1)),"b",
>> >NULL)),C3="R")
>> > lc2 <- list(C1 = "P",C2 =
>> >ifelse(is.element("Q",names(a1)),"Q",ifelse(is.element("b",names(a1)),"b",
>> >NULL)),
>> >C3=ifelse(is.element("Ra",names(a1)),"Ra",NULL))
>> >*The error for the above:*
>> >Error in ifelse(is.element("Ra", names(a1)), "Ra", NULL) :
>> >  replacement has length zero
>> >In addition: Warning message:
>> >In rep(no, length.out = length(ans)) :
>> >  'x' is NULL so the result will be NULL
>> >
>> >a2 <- subset(a1, sel=unlist(lc1)) # this works
>> >a3 <- subset(a1, sel=unlist(lc2)) # this doesn't work
>> >
>> >Is there a way to dynamically include columns in a dataframe?
>> >
>> >Regards,
>> >santosh
>> >
>> >
>> >On Fri, Jan 10, 2014 at 12:45 PM, Santosh <santosh2005 at gmail.com> wrote:
>> >
>> >> Dear Rxperts...
>> >>
>> >> I would like to conditionally include an element (as a column) in a
>> >> dataframe. Please see the  sample code below:
>> >>
>> >> a1 <-
>> >>
>> >>data.frame(P=rep(1,10),Qr=LETTERS[1:10],b=letters[1:10],R=rep(c("A","B"),
>> >>each=5))
>> >>
>> >>  lc1 <- list(C1 = "P",C2 =
>> >>
>> >>ifelse(is.element("Q",names(a1)),"Q",ifelse(is.element("b",names(a1)),"b"
>> >>,NULL)),C3="R")
>> >>  lc2 <- list(C1 = "P",C2 =
>> >>
>> >>ifelse(is.element("Q",names(a1)),"Q",ifelse(is.element("b",names(a1)),"b"
>> >>,NULL)),C3="Ra")
>> >>
>> >> a2 <- subset(a1, sel=unlist(lc1)) # this works
>> >> a3 <- subset(a1, sel=unlist(lc2)) # this doesn't
>> >>
>> >> Is there a way to dynamically include columns in a dataframe?
>> >>
>> >> Regards,
>> >> santosh
>> >>
>> >
>> >       [[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.
>>
>>
>
>         [[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.