find time windows by conditional values in a time series - r

Question

I have a very long time series. The timestamps are equidistant. For simplicity, I am leaving out many columns and rows:
library(data.table)
dt <- data.table(time = c(seq(0, 2, by = 0.1)),
value1 = c(1, 2, 1, 3, 2, 2, 1, 4, 6, 3, 2, 1, 2, 3, 2, 1, 3, 2, 3, 2, 1),
value2 = c(8, 7, 7, 6, 7, 8, 5, 6, 4, 1, 3, 2, 5, 7, 6, 8, 7, 8, 4, 1, 2))
The graph of the data look likes this:
library(ggplot2)
ggplot(data = dt, aes(x = time)) +
geom_line(aes(y = value1), color = "red", size = 2) +
geom_line(aes(y = value2), color = "blue", size = 2)
Now I want to find to find the time series windows, that fulfill specific conditions. All conditions have to be met at the same time window. In this example:
the red line (value1) must be between 1 and 3
the blue line (value2) must be between 6 and 8
the time window must have a length of AT LEAST 0.5 seconds. (for example: if there is a timeline of 2 seconds, where the value conditions are met, the timeline of 2 seconds should be returned an NOT 4 x 0.5 seconds timelines)
How am I able to implement this in R for a very long time series and multiple columns/conditions?
The goal is to find similar patterns in my data by a special set of conditions.

Answer 1

Consider this solution. It defines a window_id for every valid timestamp in a window. if a timestamp is not part of a valid window, window_id is NA.
# value constraints
dt$value_cons_met <- inrange(dt$value1,1,3) & inrange(dt$value2,6,8)
# assign all potential sequential true timestamps a group id
dt$potential_win_id <- c(0,cumsum(abs(diff(dt$value_cons_met))))
# is the window big enough?
dt[,window_size_okay := max(time)-min(time) >= 0.5 ,by = potential_win_id]
# Other window dependent constraints can be put here
# Window "ID" is defined if the valid cons are met and window size is okay
# in that case copy potential window number as window id
dt[,window_id := ifelse(value_cons_met & window_size_okay, potential_win_id,NA)]
# sample plot
library(ggplot2)
ggplot(data = dt, aes(x = time)) +
geom_line(aes(y = value1), color = "red", size = 2) +
geom_line(aes(y = value2), color = "blue", size = 2) +
geom_line(aes(y = window_id), color = "green", size =2)
This is an example plot where the detected window_id is the y value