[R] Accessing items in a list of lists

[Dimitris Rizopoulos]

check the following:

sapply(comb, "[[", "a")
# or
data.frame(
     "names" = names(comb),
     "value" = sapply(comb, "[[", "a"),
     row.names = seq_along(comb)
)


I hope it helps.

Best,
Dimitris

----
Dimitris Rizopoulos
Biostatistical Centre
School of Public Health
Catholic University of Leuven

Address: Kapucijnenvoer 35, Leuven, Belgium
Tel: +32/(0)16/336899
Fax: +32/(0)16/337015
Web: http://med.kuleuven.be/biostat/
      http://www.student.kuleuven.be/~m0390867/dimitris.htm


Quoting nalbicelli at tricadiacdpcmanagement.com:

> Using R 2.6.2, say I have the following list of lists, "comb":
>
> data1 <- list(a = 1, b = 2, c = 3)
> data2 <- list(a = 4, b = 5, c = 6)
> data3 <- list(a = 3, b = 6, c = 9)
> comb <- list(data1 = data1, data2 = data2, data3 = data3)
>
> So that all names for the lowest level list are common.  How can I most
> efficiently access all of the sublist items "a" indexed by the outer
> list names?  For example, I can loop through comb[[i]], unlisting as I
> go, and then look up the field "a", as below, but there has got to be a
> cleaner way.
>
> finaldata <- double(0)
> for(i in 1:length(names(comb))) {
> 	test <- unlist(comb[[i]])
> 	finaldata <- c(finaldata, test[which(names(test) == "a")])
> }
> data.frame(names(comb), finaldata)
>
> Gives what I want:
>   names.comb. finaldata
> 1       data1         1
> 2       data2         4
> 3       data3         3
>
> Any help you can give would be greatly appreciated.  Thanks.
> --------------------------------------------------------
>
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