I have the following code. Please see the explanation in ###. Data is two columns with Time and velocity at 10Hz sampling rate

... and so on

#create interval 
  from=min(data$Time)
  to=max(data$Time)
  breaks=seq(from, to, by=0.2)
  
  
  #function to select values in each interval and create a list, I am trying to find the highest velocity value in each interval of time BUT only IF it is greater than the value in the previous time interval 
  
  interval <- lapply(1:(length(breaks)-1L), function(i) {
    x <- subset(sprint1, Time >= breaks[i] & Time <= breaks[i 1L])
    x[x$velocity == max(x$velocity[1]), ]
  })
  
  #function to round values to two decimal places
  r <- function(x) format(round(x, 2), nsmall = 2L)
  
  #assign names to each element of interval
  for(i in seq_along(interval)) {
    names(interval)[i] <- paste0(r(breaks[i]), '-', r(breaks[i 1L]))
  }
  
  
  interval ##output

You can create dataset with Time and velocity.

CodePudding user response：

I don't think you need a list or loop. Here's my suggestion, based on my understanding of your issue:

First, define your intervals based on breaks using cut():

library(dplyr)

# Define breaks for intervals ("groups")
breaks <- seq(0, 0.28, by = 0.02)

# Group data using breaks
dat$interval <- cut(dat$Time, breaks = breaks, right = FALSE, labels = FALSE)

Now use dplyr to manipulate your data based on your condition: "find the highest velocity value in each interval of time BUT only IF it is greater than the value in the previous time interval."

dat2 <- dat %>%
  # For each group, as defined by an interval
  group_by(interval) %>%
  # Get the maximum velocity value
  mutate(interval_max = max(velocity)) %>%
  # Now ungroup and iterate across rows
  ungroup %>%
  # If the previous value is greater than the current value,
  # keep the previous value, if not, keep the current value
  mutate(interval_max_cond = ifelse(
                                 lag(interval_max) > interval_max,
                                 lag(interval_max),
                                 interval_max))

Let me know if you have any questions!

data:

dat <- structure(list(Time = c(0, 0.0099998, 0.0200003, 0.0300001, 0.0399999, 
0.0499997, 0.0600002, 0.07, 0.0799998, 0.0900003, 0.1000001, 
0.1099999, 0.1199997, 0.1300002, 0.14, 0.1499998, 0.1600003, 
0.1700001, 0.1799999, 0.1899997, 0.2000002, 0.21, 0.2199998, 
0.2300003, 0.2400001, 0.2499999, 0.2599997), velocity = c(0.3444447, 
0.3444447, 0.3444447, 0.3444447, 0.3444447, 0.3444447, 0.3444447, 
0.3444447, 0.3444447, 0.3444447, 0.3444447, 0.3444447, 0.3444447, 
0.3444447, 0.3444447, 0.3444447, 0.3444447, 0.3444447, 0.3444447, 
0.441667, 0.441667, 0.441667, 0.441667, 0.441667, 0.6222227, 
0.6222227, 0.6222227)), class = "data.frame", row.names = c(NA, 
-27L))