Re: [R] Passing a list object to lapply

Uwe Ligges Tue, 25 Aug 2009 04:11:50 -0700


Fowler, Mark wrote:

Hello,

I'm having difficulty passing an object name to a lapply function. Can
somebody tell me the trick to make this work?

lapply() works on objects rather than names of objects, hence you needget(paste(...)).


Uwe Ligges


#Works
T13702 <- TRACKDATA[["13702.xls"]][["data"]]
min(unlist(lapply(list(T13702), function(x) mdy.date(x[1, 2], x[1, 1],
x[1, 3]))))
16553

#Works
d<-2
assign(paste("T",substr(names(TRACKDATA)[d],1,(nchar(names(TRACKDATA)[d]
)-4)),sep=""),TRACKDATA[[d]][["data"]],pos=1)
min(unlist(lapply(list(T13702), function(x) mdy.date(x[1, 2], x[1, 1],
x[1, 3]))))
16553

#Fails.
d<-2
assign(paste("T",substr(names(TRACKDATA)[d],1,(nchar(names(TRACKDATA)[d]
)-4)),sep=""),TRACKDATA[[d]][["data"]],pos=1)
min(unlist(lapply(list(paste("T",substr(names(TRACKDATA)[d],1,(nchar(nam
es(TRACKDATA)[d])-4)),sep="")), function(x) mdy.date(x[1, 2], x[1, 1],
x[1, 3]))))
Error in x[1, 2] : incorrect number of dimensions

traceback()

4: mdy.date(x[1, 2], x[1, 1], x[1, 3])
3: FUN(X[[1L]], ...)
2: lapply(list(paste("T", substr(names(TRACKDATA)[d], 1,

(nchar(names(TRACKDATA)[d]) -4)), sep = "")), function(x) mdy.date(x[1, 2], x[1, 1], x[1,3]))1: unlist(lapply(list(paste("T", substr(names(TRACKDATA)[d], 1,(nchar(names(TRACKDATA)[d]) - 4)), sep = "")), function(x)mdy.date(x[1,2], x[1, 1], x[1, 3])))


#Fails (trying noquote).
min(unlist(lapply(list(noquote(paste("T",substr(names(TRACKDATA)[d],1,(n
char(names(TRACKDATA)[d])-4)),sep=""))), function(x) mdy.date(x[1, 2],
x[1, 1], x[1, 3]))))
Error in unclass(x)[...] : incorrect number of dimensions

traceback()

6: `[.noquote`(x, 1, 2)
5: x[1, 2]
4: mdy.date(x[1, 2], x[1, 1], x[1, 3])
3: FUN(X[[1L]], ...)

2: lapply(list(noquote(paste("T", substr(names(TRACKDATA)[d], 1,(nchar(names(TRACKDATA)[d]) - 4)), sep = ""))), function(x)mdy.date(x[1,2], x[1, 1], x[1, 3]))1: unlist(lapply(list(noquote(paste("T", substr(names(TRACKDATA)[d],1, (nchar(names(TRACKDATA)[d]) - 4)), sep = ""))), function(x)mdy.date(x[1,2], x[1, 1], x[1, 3])))

        Mark Fowler

                Population Ecology Division

        Bedford Inst of Oceanography
        Dept Fisheries & Oceans
        Dartmouth NS Canada

                B2Y 4A2
                Tel. (902) 426-3529
                Fax (902) 426-9710
                Email fowl...@mar.dfo-mpo.gc.ca
                Home Tel. (902) 461-0708
                Home Email mark.fow...@ns.sympatico.ca



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Re: [R] Passing a list object to lapply

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