DATA = data.table(STUDENT = c(1,1,2,2,2,2,2,3,3,3,3,3,4,
SCORE = c(5,6,8,3,14,5,6,9,0,12,13,14,19))
WANT = data.table(STUDENT = c(1,1,4),
SCORE = c(5,6,19))
I have DATA and wish to create WANT which takes a random sample of 2 STUDENT and includes all of their data. I present WANT as an example.
I try this with no success
WANT = WANT[ , .SD[sample(x = .N, size = 2)], by = STUDENT]
>Solution :
sample the unique values of STUDENT and filter all the rows for those STUDENT,
library(data.table)
set.seed(1357)
DATA[STUDENT %in% sample(unique(STUDENT), 2)]
# STUDENT SCORE
#1: 1 5
#2: 1 6
#3: 4 19