在data.table中熔化时，如何不丢失所有未熔化的列？

library(data.table)

# 创建一个示例data.table
dt <- data.table(
  id = 1:5,
  name = c("Alice", "Bob", "Charlie", "David", "Eve"),
  age = c(25, 30, 35, 40, 45),
  score_math = c(90, 85, 95, 80, 75),
  score_science = c(85, 90, 80, 95, 70)
)

# 熔化data.table，并保留未熔化的列
melted_dt <- melt(dt, id.vars = c("id", "name", "age"))

# 打印结果
print(melted_dt)

   id    name age      variable value
1:  1   Alice  25   score_math    90
2:  2     Bob  30   score_math    85
3:  3 Charlie  35   score_math    95
4:  4   David  40   score_math    80
5:  5     Eve  45   score_math    75
6:  1   Alice  25 score_science    85
7:  2     Bob  30 score_science    90
8:  3 Charlie  35 score_science    80
9:  4   David  40 score_science    95
10: 5     Eve  45 score_science    70