reject numbers in a sequence of numbers that do not increase with same increase

Question

I have a sequence of numbers that I want to check and reject numbers that do not increase with similar level.

data <- c(1, 2, 5, 6, 6.25, 6.49, 6.75, 7.01, 8, 9, 11)

For example, for the data here I want to subset numbers with an increase of 0.25+/-0.1, and reject numbers that do not follow this rule. In this case, the subseted sequence would be (6, 6.25, 6.49, 6.75, 7.01).

Answer 1

Here's an ugly way to grab the indexes that you want to keep. Change 0.35 if you're interested in a different cutoff value

myfun <- function(D) {
            index <- unique(c(which(abs(diff(D)) < 0.35), which(abs(diff(D)) < 0.35)+1))
            return(sort(index))
        }

Call the function to obtain the answer you want with

data[myfun(data)]
# [1] 6.00 6.25 6.49 6.75 7.01

Another test

test <- c(1, 1.25, 2, 2.25, 3, 4.5, 4.75, 5, 5.45, 5.65)
test[myfun(test)]
# [1] 1.00 1.25 2.00 2.25 4.50 4.75 5.00 5.45