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

Alternative solutions for list of matrix or dataframe

Alternative solutions for list of 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 1
result1.1 <- 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 R
library(plyr)
result1.2.1 <- ldply(myList1, rbind)
head(result1.2.1)
###Error: All inputs to rbind.fill must be data.frames
result1.2.2 <- 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.frame
library(data.table)
###Error in rbindlist(myList1) : Item 1 of list input is not a data.frame, data.table or list
result1.3 <- 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.time
library(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 list
myList3 <- 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 list
tempList <- 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)