Random Sample with Replacement Loop - r

Question

I have an R script that allows me to select a sample size and take fifty individual random samples with replacement. Below is an example of this code:
## Creates data frame
df = as.data.table(data)
## Select sample size
sample.size = 5
## Creates Sample 1 (Size 5)
Sample.1<-df[,
Dollars[sample(.N, size=sample.size, replace=TRUE)], by = Num]
Sample.1$Sample <- c("01")
According to the R script above, I first created a data frame. I then select my sample size, which in this case is 5. This represents just one sample. Due to my lack of experience with R, I repeat this code 49 more times. The last piece of code looks like this:
## Creates Sample 50 (Size 5)
Sample.50<-df[,
Dollars[sample(.N, size=sample.size, replace=TRUE)], by = Num]
Sample.50$Sample <- c("50")
The sample output would look something like this (Sample Range 1 - 50):
Num Dollars Sample
1 85000 01
1 4900 01
1 18000 01
1 6900 01
1 11000 01
1 8800 50
1 3800 50
1 10400 50
1 2200 50
1 29000 50
It should be noted that varaible 'Num' was created for grouping purposes and has little to no influence on my overall question (which is posted below).
Instead of repeating this code fifty times, to get me fifty individual samples (with a size of 5), is there a loop I can create to help me limit my code? I have been recently asked to create ten thousand random samples, each of a size of 5. I obviously cannot repeat this code ten thousand times so I need some sort of loop.
A sample of my final output should look something like this (Sample Range 1 - 10,000):
Num Dollars Sample
1 85000 01
1 4900 01
1 18000 01
1 6900 01
1 11000 01
1 9900 10000
1 8300 10000
1 10700 10000
1 6800 10000
1 31000 10000
Thank you all in advance for your help, its greatly appreciated.
Here is some sample code if needed:
Num Dollars
1 31002
1 13728
1 23526
1 80068
1 86244
1 9330
1 27169
1 13694
1 4781
1 9742
1 20060
1 35230
1 15546
1 7618
1 21604
1 8738
1 5299
1 12081
1 7652
1 16779

Answer 1

A very simple method would be to use a for loop and store the results in a list:
lst <- list()
for(i in seq_len(3)){
lst[[i]] <- df[sample(seq_len(nrow(df)), 5, replace = TRUE),]
lst[[i]]["Sample"] <- i
}
> lst
[[1]]
Num Dollars Sample
20 1 16779 1
1 1 31002 1
12 1 35230 1
14 1 7618 1
14.1 1 7618 1
[[2]]
Num Dollars Sample
9 1 4781 2
13 1 15546 2
12 1 35230 2
17 1 5299 2
12.1 1 35230 2
[[3]]
Num Dollars Sample
1 1 31002 3
7 1 27169 3
17 1 5299 3
5 1 86244 3
6 1 9330 3
Then, to create a single data.frame, use do.call to rbind the list elements together:
do.call(rbind, lst)
Num Dollars Sample
20 1 16779 1
1 1 31002 1
12 1 35230 1
14 1 7618 1
14.1 1 7618 1
9 1 4781 2
13 1 15546 2
121 1 35230 2
17 1 5299 2
12.1 1 35230 2
11 1 31002 3
7 1 27169 3
171 1 5299 3
5 1 86244 3
6 1 9330 3

Answer 2

It's worth noting that if you're sampling with replacement, then drawing 50 (or 10,000) samples of size 5 is equivalent to drawing one sample of size 250 (or 50,000). Thus I would do it like this (you'll see I stole a line from #beginneR's answer):
df = as.data.table(data)
## Select sample size
sample.size = 5
n.samples = 10000
# Sample and assign groups
draws <- df[sample(seq_len(nrow(df)), sample.size * n.samples, replace = TRUE), ]
draws[, Sample := rep(1:n.samples, each = sample.size)]