It is possible to chain together uses of `[[` -- e.g., x <- list(1:5, list(letters[1:5], list(LETTERS[1:5])))
x[[c(1,2)]] # 2L x[[c(2,1,3)]] # "c" x[[c(2,2,1,3)]] # "C" which is sometimes useful. Best, Michael On Mon, Jun 11, 2012 at 4:35 PM, Onur Uncu <onuru...@gmail.com> wrote: > Rui and the R-help team, > > In Rui's helpful answer below, the function returns a list as output. > When we apply() the function to the data.frame, dataframe$newcolumn > has 2 layers of list before we can access each vector elements. For > instance, dataframe$newcolumn[[1]][[1]] is a vector whereas > dataframe$newcolumn and dataframe$newcolumn[[1]] are lists. Is there a > solution that involves less layers of lists? I am just trying to > understand the R language better. > > Thank you. > > > On Sun, Jun 10, 2012 at 3:18 PM, Rui Barradas <ruipbarra...@sapo.pt> wrote: >> Hello, >> >> What you need is to have your function return a list, not a vector. Like >> this >> >> testfun <- function (x, y) list(seq(x, y, 1)) >> >> testframe<-data.frame(xvalues=c(2,3),yvalues=c(4,5)) >> >> testframe$newcolumn <- apply(testframe, 1, function(x) testfun(x[1], x[2])) >> class(testframe$newcolumn) # [1] "list" >> >> Then you access lists and list elements. >> >> testframe$newcolumn[[1]] # a list with just one element >> testframe$newcolumn[[1]][[1]] # that element, a vector >> testframe$newcolumn[[1]][[1]][2] # the vector's 2nd element >> >> >> Since you want the function to return vectors in order to do further >> computations, you'll access those vectors by varying the list index, >> >> >> testframe$newcolumn[[1]][[1]] # first list, it's only vector >> testframe$newcolumn[[2]][[1]] # second list, it's only vector >> >> >> Etc. >> >> Hope this helps, >> >> Rui Barradas >> >> Em 10-06-2012 12:29, Onur Uncu escreveu: >>> >>> Thank you Duncan. A follow-up question is, how can I achieve the >>> desired result in the earlier email? (i.e. Add the resulting vectors >>> as a new column to the existing data.frame?) I tried the following: >>> >>> testframe$newcolumn<-apply(testframe,1,function(x)testfun(x[1],x[2])) >>> >>> but I am getting the following error: >>> >>> Error in `$<-.data.frame`(`*tmp*`, "vecss", value = c(2, 3, 4, 3, 4, 5 >>> : replacement has 3 rows, data has 2 >>> >>> Thanks for the help. >>> >>> >>> On Sun, Jun 10, 2012 at 12:02 PM, Duncan Murdoch >>> <murdoch.dun...@gmail.com> wrote: >>>> >>>> On 12-06-10 6:41 AM, Onur Uncu wrote: >>>>> >>>>> >>>>> R-Help community, >>>>> >>>>> I understand that data.frames can hold elements of type double, string >>>>> etc but NOT objects (such as a matrix etc). >>>> >>>> >>>> >>>> That is incorrect. Dataframes can hold list vectors. For example: >>>> >>>> A <- data.frame(x = 1:3) >>>> A$y <- list(matrix(1, 2,2), matrix(2, 3,3), matrix(3,4,4)) >>>> >>>> A[1,2] will now extract the 2x2 matrix, A[2,2] will extract the 3x3, etc. >>>> >>>> Duncan Murdoch >>>> >>>> This is not convenient for >>>>> >>>>> >>>>> me in the following situation. I have a function that takes 2 inputs >>>>> and returns a vector: >>>>> >>>>> testfun<- function (x,y) seq(x,y,1) >>>>> >>>>> I have a data.frame defined as follows: >>>>> >>>>> testframe<-data.frame(xvalues=c(2,3),yvalues=c(4,5)) >>>>> >>>>> I would like to apply testfun to every row of testframe and then >>>>> create a new column in the data.frame which holds the returned vectors >>>>> as objects. Why do I want this? Because the returned vectors are an >>>>> intermediate step towards further calculations. It would be great to >>>>> keep adding new columns to the data.frame with the intermediate >>>>> objects. But this is not possible since data.frames can not hold >>>>> objects as elements. What do you suggest as an elegant solution in >>>>> this scenario? Thank you for any help! >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> I would love to hear if forum >>>>> >>>>> ______________________________________________ >>>>> R-help@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@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@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@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.
