time differences between rows without night in R - r

Question

A subject was measured at several time points over several days. I have a row "resptime_s" (time that the subject was answered the beep on his smartphone). Now I want to know the mean time between those (so between the rows of this column) with the night time taken out (nighttime is always from 22:30 p.m till 7:30 a.m). Take as example:
The R script:
setwd("C:/Users/Hanne/Desktop/")
dat <- read.csv(file="datnew2.csv", sep=";",header=TRUE)
rows <- c(1:388) #time points
columns <- c(2,60) # datum and time
nVariables = 2
newdata<-dat[rows,columns]
head(newdata)
fun2 <- function(x){
bt <- as.integer(sub("(^\\d{1,2}):.*", "\\1", x))
f <- cumsum(c(FALSE, diff(bt) < 0))
d <- rep(as.Date("2018-01-01"), length.out = length(bt))
bt <- as.POSIXct(paste(d, x))
res <- sapply(split(bt, f), function(b) c(0, difftime(b[-1], b[1])))
unname(unlist(res))
}
fun2(newdata$resptime_s)
But the result isn't correct.
And with:
dput(head(newdata, 30))
I obtained this output:

Answer 1

Using the different functions for working with time intervals in lubridate gives the most elegant and easy to understand solution.
library(tidyverse)
library(lubridate)
data <- tribble(
~time_point, ~beeptime,
1, "08:30",
2, "11:13",
3, "12:08",
4, "17:20",
5, "22:47",
6, "7:36",
7, "9:40"
) %>%
mutate(beeptime = as_datetime(hm(beeptime)))
1. Define the daytime interval
day <- interval(
as_datetime(hm("07:30")),
as_datetime(hm("22:30"))
)
2. Keep daytime beeps and estimate the time (interval) between them
# %--% is basically the same as interval() above.
data_interval <-
data %>%
filter(beeptime %within% day) %>%
mutate(beep_interval = lag(beeptime) %--% beeptime)
3. Take the average
# You can use as.numeric() to extract (e.g.) minutes, which you can
# just pass to mean().
data_interval$beep_interval %>%
as.numeric("minutes") %>%
abs() %>%
mean(na.rm = TRUE)
#> [1] 247.6

Answer 2

Try the following. It pastes a date that increments every time the next hour is less than the previous one. Then difftime works as expected.
fun <- function(x){
bt <- as.integer(sub("(^\\d{1,2}):.*", "\\1", x))
inx <- as.logical(cumsum(c(FALSE, diff(bt) < 0)))
d <- rep(as.Date("2018-01-01"), length.out = length(bt))
d[inx] <- d[inx] + 1
beeptime <- as.POSIXct(paste(d, x))
difftime(beeptime[-1], beeptime[1])
}
fun(newdata$beeptime)
#Time differences in hours
#[1] 2.716667 3.633333 8.833333 14.283333 23.100000 25.166667
Data.
newdata <-
structure(list(time_point = 1:7, beeptime = structure(1:7, .Label = c("08:30",
"11:13", "12:08", "17:20", "22:47", "7:36", "9:40"), class = "factor")), class = "data.frame", row.names = c(NA,
-7L))
Edit.
I believe that I have missunderstood the question. The OP does not want differences between the first hour and all others. What is needed is the differences restarting from zero every night.
If this is the case, the following function will do it.
fun2 <- function(x){
bt <- as.integer(sub("(^\\d{1,2}):.*", "\\1", x))
f <- cumsum(c(FALSE, diff(bt) < 0))
d <- rep(as.Date("2018-01-01"), length.out = length(bt))
bt <- as.POSIXct(paste(d, x))
res <- sapply(split(bt, f), function(b) c(0, difftime(b[-1], b[1])))
unname(unlist(res))
}
fun2(newdata$beeptime)
#[1] 0.000000 2.716667 3.633333 8.833333 14.283333 0.000000 2.066667

Answer 3

Another approach could be to convert beeptime in offset (in seconds) from midnight using lubridate package.
We can then write a function(s) to calculate difference in time excluding night time (22:30 - 7:30).
Before we start solution, lets have a look for offset in seconds from midnight for 7:30 and 22:30.
library(lubridate)
as.numeric(seconds(hm("7:30")))
# [1] 27000
as.numeric(seconds(hm("22:30")))
# [1] 81000
I have written two sets of function to calculate difference between two times:
# Function checks individual time and shifts them to night boundary. So that
# time over night can be excluded.
checkNightBoundry <- function(val){
if(val < 27000){
val = 27000
} else if(val > 81000) {
val = 81000
}
val
}
# Arguments are offset from midnight in seconds
# Calculate difference between two time, excluding midtime
calcDifftime <- function(currVal, prevVal){
diffTime <- 0
currVal = checkNightBoundry(currVal)
prevVal = checkNightBoundry(prevVal)
if(currVal > prevVal){
diffTime = currVal - prevVal
}else if(currVal < prevVal){
diffTime = (81000 - prevVal) + (currVal - 27000)
}
diffTime
}
Now, use above functions:
library(dplyr)
library(lubridate)
df %>% mutate(beeptimeOffset = as.numeric(seconds(hm(beeptime)))) %>%
mutate(diffTime = mapply(calcDifftime,
beeptimeOffset, lag(beeptimeOffset, default = first(beeptimeOffset)))/3600)
# timepoint beeptime beeptimeOffset(sec) diffTime(hrs)
# 1 1 08:30 30600 0.0000000
# 2 2 11:13 40380 2.7166667
# 3 3 12:08 43680 0.9166667
# 4 4 17:20 62400 5.2000000
# 5 5 22:47 82020 5.1666667
# 6 6 7:36 27360 0.1000000
# 7 7 9:40 34800 2.0666667
Data:
df <- read.table(text =
"timepoint beeptime
1 08:30
2 11:13
3 12:08
4 17:20
5 22:47
6 7:36
7 9:40",
header = TRUE, stringsAsFactors = FALSE)