下列数据:
df <- data.frame(cbind("Group_ID" = c(1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4), "WBHO" = runif(20, 1.0, 7.0), "SI" = runif(20, 1.0, 7.0), "OORT" = c(2.34, 4.64, NA, 5.32, 3.23, 6.01, 5.43, 4.78, 3.98, 3.80, 4.45, NA, NA, 3.18, 4.87, NA, NA,