[R] Bind element of List of matrix or data.frame or list

1. Alternative solutions for list of matrix or data.frame

If I have a list of matrix or data.frame, we can use the following ways to bind the rows of all elements.

Firstly, I generate toy data

myList1 <- list(matrix(rnorm(2*3), ncol=2),                matrix(rnorm(2*3), ncol=2),                matrix(rnorm(2*3), ncol=2),                matrix(rnorm(2*3), ncol=2))myList2 <- list(as.data.frame(matrix(rnorm(2*3), ncol=2)),                as.data.frame(matrix(rnorm(2*3), ncol=2)),                as.data.frame(matrix(rnorm(2*3), ncol=2)),                as.data.frame(matrix(rnorm(2*3), ncol=2)))

Now I list the alternative solutions

# solution 1result1.1 <- do.call(rbind, myList1)head(result1.1)result1.2 <- do.call(rbind, myList2)head(result1.2)# solution 2## plyr: the split-apply-combine paradigm for Rlibrary(plyr)result1.2.1 <- ldply(myList1, rbind)head(result1.2.1)###Error: All inputs to rbind.fill must be data.framesresult1.2.2 <- rbind.fill(myList1)head(result1.2.2)result2.2.1 <- ldply(myList2, rbind)head(result2.2.1)result2.2.2 <- rbind.fill(myList2)head(result2.2.2)# solution 3## data.table: Enhanced data.framelibrary(data.table)###Error in rbindlist(myList1) : Item 1 of list input is not a data.frame, data.table or listresult1.3 <- rbindlist(myList1)head(result1.3)result2.3 <- rbindlist(myList2)head(result2.3)

From the codes, we can see that

• for matrix, only do.call(rbind, ), ldply can work.
• for data.frame, all do.call(rbind, ), ldply, rbind.fill, rbindlist can work.

And now benchmark for all solutions

# benchmark## benchmark: a simple wrapper around system.timelibrary(rbenchmark)benchmark(do.call(rbind, myList2), ldply(myList2, rbind), rbind.fill(myList2), rbindlist(myList2))

2. Alternative solutions for list of list

#############list of list############################## generate list of listmyList3 <- vector("list", 4)for(i in 1:4){  myList3[[i]] <- vector("list", 2)  for(j in 1:2){    myList3[[i]][[j]] <- rnorm(3)  }}# bind each element of outer listtempList <- lapply(myList3, function(z)do.call(rbind,z))## selection operator "["bind.ith.rows <- function(i) do.call(rbind, lapply(tempList, "[", i, TRUE))nr <- nrow(tempList[[1]])lapply(1:nr, bind.ith.rows)