On May 26, 2015, at 3:59 PM, blue honour via R-help wrote:
> Dear R users,
> I have a question regarding retrieving data from nested lists. To illustrate,
> here is an example input:
> d1<-data.table(v1=c(3,4),v2=c(2,5))
> d2<-data.table(v1=c(1,2),v2=c(1,1))l1<-list(d1,name="test")l2<-list(d2,name="test2")motherlist<-list()motherlist$l1<-l1motherlist$l2<-l2
> Let's say we are given motherlist as above. We would like to get the union of
> the contents of v1 vector from d1 data.table and the v1 vector from d2
> data.table. How can we achieve this in a compact one line command using
> motherlist as input please?
> Thank you.
>
>
>
> [[alternative HTML version deleted]]
Your posting is a good example of the reason we ask people _not_ to post in
HTNL. Linefeeds (among many other useful bits of information) get lost:
d1<-data.table(v1=c(3,4),v2=c(2,5))
d2<-data.table(v1=c(1,2),v2=c(1,1))
l1<-list(d1,name="test")
l2<-list(d2,name="test2")
motherlist<-list()
motherlist$l1<-l1
motherlist$l2<-l2
> with( motherlist, c( l1[1][[1]]$v1, l2[1][[1]]$v1) )
[1] 3 4 1 2
OR:
> with( motherlist, c( l1[[1]]$v1, l2[[1]]$v1) )
[1] 3 4 1 2
That used the inheritance of data.tables from data.frames. This is data.table
extraction syntax:
> with( motherlist, c( l1[[1]][ ,v1], l2[[1]][ ,v1]) )
[1] 3 4 1 2
Another approach with the display of intermediate values:
> sapply(motherlist, "[", 1)
$l1
v1 v2
1: 3 2
2: 4 5
$l2
v1 v2
1: 1 1
2: 2 1
> sapply( sapply(motherlist, "[", 1) , "[[", 1)
l1 l2
[1,] 3 1
[2,] 4 2
> c( sapply( sapply(motherlist, "[", 1) , "[[", 1) )
[1] 3 4 1 2
Please read the posting guide.
>
> ______________________________________________
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> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
David Winsemius
Alameda, CA, USA
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