[R] merge list entries

alejandro munoz guerinche at gmail.com
Tue Aug 23 22:01:14 CEST 2005

dear expeRts,

i would like to merge the data frame entries in a list. for example:

> #input
> myl <- list(q1=data.frame(id=c("Alice", "Bob"), grade=c(90, 49)),
              q2=data.frame(id=c("Alice", "Chuck"), grade=c(70, 93)),
              q3=data.frame(id=c("Bob", "Chuck"), grade=c(84, 40)))
> #output
> (mydf <- magic(myl))
      id grade.1 grade.2 grade.3
1 Alice      90      70      NA
2   Bob      49      NA      84
3 Chuck      NA      93      40

my three attempts, and their error messages, follow:
> lapply(myl, merge, by="id", all=TRUE)
Error in as.data.frame(y) : argument "y" is missing, with no default

> lapply(myl[[-1]], merge, y=myl[[1]], by="id", all=TRUE)
Error in lapply(myl[[-1]], merge, y = myl[[1]], by = "id", all = TRUE) : 
	attempt to select more than one element

> do.call("merge", list(myl[[1]], myl[[-1]], by="id", all=TRUE))
Error in do.call("merge", list(myl[[1]], myl[[-1]], by = "id", all = TRUE)) : 
	attempt to select more than one element

i can do the merge sequentially, e.g. 
m12 <- merge(myl[[1]], myl[[2]], ...)
m123 <- merge(m12, myl[[3]], ...)
but (a) in my actual example i have up to q7, and (b) this looks very
clumsy, even if i wrapped it inside a do loop.

i'd appreciate any help.


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