r - create a sample matrix from the main matrix

I want to create a sample matrix from the main one with the sam number of columns but less rows (50) I tried to use a series of loops but it didn't work:

n=nrow(data)
camp <- sample(1:n,size=50,replace=TRUE)



n<-length(camp)
c<-ncol(data)
for(i in 1:n){
      t<-camp[i]
    for(k in 1:c){
    campione[i,k]<-data[t,k]}
}

Answer

You don't need to use loop. You just have to take random lines from your main matrix:

mat = matrix(runif(2000),ncol=20)

sample_matrix = mat[sample(1:nrow(mat),50),]