R-循环-使用上一行中的值

Question

我对R比较陌生，希望在for循环中寻求帮助...所以我有一个包含许多时间点的变量，并且每个时间点都有对应的另一个变量的等级（复杂度为1-9），我想要一个一个新变量，它告诉我复杂性等级开始和结束的时间点，以及它们何时更改。任何帮助最欢迎！这是我的最大努力，但它会返回所有时间点！

`Structure(list(Replicate = c(1L, 1L, 1L, 1L, 1L, 1L), Stimulus = c(1L, 
1L, 1L, 1L, 1L, 1L), Subject = c("S001", "S001", "S001", "S001", 
"S001", "S001"), Attribute = c("Soft", "Soft", "Soft", "Soft", 
"Soft", "Soft"), Timepoint = c("t0.77", "t0.78", "t0.79", "t0.8", 
"t0.81", "t0.82"), Dominant = c(1L, 1L, 1L, 1L, 1L, 1L), Complexity = 
c(2L,2L, 2L, 2L, 2L, 2L)`

Answer 1

dataframe.df$start_end_time <- c(dataframe.df$Timepoint[1], dataframe.df$Timepoint[which(diff(dataframe.df$Complexity) == 0)])