sample rows from dataframe using for loop in R

Question

There is a df given with nrow=600 and ncol=18

Now I need to sample 10000 of each of this columns with replacement.

According to the specifications first I need to create an empty matrix:

df1 <- as.data.frame(matrix(NA,nrow = 10000,ncol=18))

now I want to use for loop to do all the samples(for each column) at once:

for (i in 1:18){

df1[1:10000, i) <- sample(df[,i], 10 000, replace=true)

when I run this code, my df1 is still empty.

Can anyone help?

Many thanks in advance

Answer 1

There are syntax issues in your code. Try the following :

df1 <- as.data.frame(matrix(NA,nrow = 10000,ncol=18))

for (i in 1:18) {
  df1[, i] <- sample(df[, i], 10000, replace = TRUE)
}

Without an explicit for loop you can also use sapply/lapply :

#With `sapply`
df1 <- as.data.frame(sapply(df, sample, 1000, replace = TRUE))

#Using `lapply`

df1 <- do.call(cbind.data.frame, lapply(df, sample, 1000, replace = TRUE))

---

It works for the data shared in comments.

df <- data.frame(V1, V2, V3)
df1 <- as.data.frame(matrix(NA,nrow = 10000,ncol=3))

for (i in 1:3) {
  df1[, i] <- sample(df[, i], 10000, replace = TRUE)
}

dim(df1)
#[1] 10000     3

head(df1)
#           V1           V2           V3
#1  0.02527926  0.039423826  0.097738594
#2  0.03391239  0.039423826  0.036153091
#3  0.03919354 -0.004922473  0.097738594
#4 -0.06703827  0.039423826  0.097738594
#5  0.02168909  0.048176052  0.036153091
#6  0.02527926  0.074435079 -0.009444024