How to make the loop faster? - r

Question

My code looks as below, I am wondering if there any better way to make it faster:
pos=NULL
row=data.frame(matrix(nrow=216,ncol=4))
colnames(row)=c("sub","subi","group","trial")
for (i in 1:100000){
row$sub="Positive"
row$subi=NA
row$group=NA
row$subi[1:144]=c(1:144)
row$group[1:144]=1
row$subi[145:216]=c(1:72)
row$group[145:216]=2
row$trial=i
pos=rbind(pos,row)
}

Answer 1

No loop needed. You can build a data.frame or tibble(my example) on your own.
Given you want to adjust the row length later:
library(dplyr)
n_rows <- 10000
tibble(
trail = 1:n_rows,
sub = "positive",
subi = c(seq(1:144), seq(1:72), rep(NA, n_rows-216)),
group = c(rep(1, 144), rep(2, 72), rep(NA, n_rows-216))
)
Output is:
# A tibble: 10,000 × 4
trail sub subi group
<int> <chr> <int> <dbl>
1 1 positive 1 1
2 2 positive 2 1
3 3 positive 3 1
4 4 positive 4 1
5 5 positive 5 1
6 6 positive 6 1
7 7 positive 7 1
8 8 positive 8 1
9 9 positive 9 1
10 10 positive 10 1
# … with 9,990 more rows

Answer 2

The only thing different in each pass of the loop is trial. rep is your friend. For the other columns, R will automatically recycle to match the longest column (here, it is trial with 21.6M rows).
pos <- data.frame(
sub = "Positive",
subi = c(1:144, 1:72),
group = rep.int(1:2, c(144, 72)),
trial = rep(1:1e5, each = 216)
)

Answer 3

It looks like you are trying to replicate this data frame 100,000 times, with each iteration of the frame having a different trial number.
data.frame(sub = rep("Positive", 216),
subi = c(1:144, 1:72),
group = rep(c(1, 2), c(144, 72)))
The replicate function is great for running static code multiple time. So one option is to create your 100,000 copies and then update the trial number.
FrameList <-
replicate(n = 100,
{
data.frame(sub = rep("Positive", 216),
subi = c(1:144, 1:72),
group = rep(c(1, 2), c(144, 72)),
trial = rep(NA_real_, 216))
},
simplify = FALSE)
To update the trial number, you can go with a for loop
for (i in seq_along(FrameList)){
FrameList$trial <- i
}
or you can try something fancy-pants, but taking a lot more code
FrameList <- mapply(function(FL, i){
FL$trial <- i
FL
},
FrameList,
seq_along(FrameList),
SIMPLIFY = FALSE)
Whichever way you go, you can stack them all together with
Frame <- do.call("rbind", FrameList)
This certainly isn't the most elegant way to do this, so watch for others to give you other clever tricks. But this, I would guess, would be the basic process to follow.