unlist and merge selected columns to data frame in R - r

Question

Suppose I have a list such like:
df1<-data.frame(n=letters[1:4], x=1:4, y=2:5, z=3:6)
df2<-data.frame(n=letters[2:5], x=2:5, y=3:6, z=4:7)
df3<-data.frame(n=letters[3:7], x=2:6, y=3:7, z=4:8)
ls<-list(df1, df2, df3)
ls
[[1]]
n x y z
1 a 1 2 3
2 b 2 3 4
3 c 3 4 5
4 d 4 5 6
[[2]]
n x y z
1 b 2 3 4
2 c 3 4 5
3 d 4 5 6
4 e 5 6 7
[[3]]
n x y z
1 c 2 3 4
2 d 3 4 5
3 e 4 5 6
4 f 5 6 7
5 g 6 7 8
what I wanted is to merger the first two columns of each data frame in the list by column n and a desired output would be:
n x1 x2 x3
1 a 1 NA NA
2 b 2 2 NA
3 c 3 3 2
4 d 4 4 3
5 e NA 5 4
6 f NA NA 5
7 g NA NA 6
And same thing for y and z:
n y1 y2 y3
1 a 2 NA NA
2 b 3 3 NA
3 c 4 4 3
4 d 5 5 4
5 e NA 6 5
6 f NA NA 6
7 g NA NA 7
n z1 z2 z3
1 a 3 NA NA
2 b 4 4 NA
3 c 5 5 4
4 d 6 6 5
5 e NA 7 6
6 f NA NA 7
7 g NA NA 8

Answer 1

We get the unique column names from the list of data.frames except the 'n' ('nm1'), loop through those (lapply(nm1,...), subset the columns of each of the 'data.frame' in 'ls' (lapply(ls, function(x) ...), and use Reduce, with merge to merge the datasets in the list.
nm1 <- setdiff(unlist(lapply(ls, names)), "n")
lapply(nm1, function(nm) setNames(Reduce(function(...)
merge(..., all=TRUE, by = "n"), lapply(ls,
function(x) x[c("n", nm)])), make.unique(c("n", rep(nm, length(nm1))))))
#[[1]]
# n x x.1 x.2
#1 a 1 NA NA
#2 b 2 2 NA
#3 c 3 3 2
#4 d 4 4 3
#5 e NA 5 4
#6 f NA NA 5
#7 g NA NA 6
#[[2]]
# n y y.1 y.2
#1 a 2 NA NA
#2 b 3 3 NA
#3 c 4 4 3
#4 d 5 5 4
#5 e NA 6 5
#6 f NA NA 6
#7 g NA NA 7
#[[3]]
# n z z.1 z.2
#1 a 3 NA NA
#2 b 4 4 NA
#3 c 5 5 4
#4 d 6 6 5
#5 e NA 7 6
#6 f NA NA 7
#7 g NA NA 8
NOTE: ls is a function name that lists the objects. It is better to avoid naming objects with known R functions.

Answer 2

Here is another base R method that uses do.call, data.frame, and cbind within a nested pair of lapply functions.
# get all levels of n across data frames
allN <- unique(unlist(sapply(ls, "[[", "n")))
# extract desired columns and provide names with setNames
lapply(names(ls[[1]])[-1], function(var) {
cbind("n"=allN, setNames(do.call(data.frame,
lapply(seq_along(ls), function(i) {
ls[[i]][[var]][match(allN, ls[[i]]$n, nomatch=NA)]
})), paste0(var, seq_along(ls))))
})
The first lapply runs through each of the variable names, the second lapply extracts the current variable from the each data frame in the list. In the middle, do.call makes the list a data.frame, setNames provides the desired names, and the n column is added with cbind.
In the innermost portion of the inner lapply, the code ls[[i]][[var]][match(allN, ls[[i]]$n, nomatch=NA)] is used to expand (and potentially reorder) the current vector according to the levels in allN. If the current vector is missing a level, the nomatch=NA tells match to instead return NA.