我正在处理一个数据集,其中许多受试者在一段时间内进行了后续判断.每次考试的年龄都有记录:
subject <- c("subject1", "subject1", "subject2", "subject2", "subject2", "subject3", "subject3")
ageAtExam <- c(50, 51, 30, 32, 35, 40, 45)
df <- data.frame(subject, ageAtExam)
> df
subject ageAtExam
1 subject1 50
2 subject1 51
3 subject2 30
4 subject2 32
5 subject2 35
6 subject3 40
7 subject3 45
我想创建一个新的列,其中给出了第一次判断的年龄(即每subject
岁的最小值为ageAtExam
):
subject ageAtExam ageAtFirstExam
1 subject1 50 50
2 subject1 51 50
3 subject2 30 30
4 subject2 32 30
5 subject2 35 30
6 subject3 40 40
7 subject3 45 40
感谢您的建议,谢谢!