How to input only increase data into an empty data frame

Question

I now need to deal with a set of experimental data where the data trend goes up and down and up and down again, for example：

List = [0,1,2,3,4,3,2,3,4,5,6,7,6,4,5,8,9]

I want my dataset to end up looking like this:

AList = [0,1,2,3,4,(remove 3,2,3,4,) 5,6,7,*(remove 6,4,5,)*8,9]

which is

AList = [0,1,2,3,4,5,6,8,9]

Does everyone have any good ideas?

I tried to use a for loop like:

AList=matrix(ncol=1)
list <- c(0,1,2,3,4,3,2,3,4,5,6,7,6,4,5,8,9)
for (i in seq(1, length(list))){
  if (list[i] < list[i+1]) {
    AList[i] = list[i]
  } else {
    list[i]=list[i+1]
  }
}
AList

But I get an error message like this：

Error in if (list[i] <= list[i + 1]) { : 
  missing value where TRUE/FALSE needed

Then I changed it to this：

for (i in seq(1, length(list))){
  if (list[i] < is.na(list[i+1])) {
    AList[i] = list[i]
  } else {
    list[i]=is.na(list[i+1])
  }
}

Then I get a result that is exactly the same as the list.

Answer 1

Filter to values greater than the lagged cumulative maximum:

library(dplyr)

list1[list1 > dplyr::lag(cummax(list1), default = -Inf)]
# 0 1 2 3 4 5 6 7 8 9