CODEWITHSUNDEEP
rtimemeanstandard-deviation
psycho95
psycho95

Reputation: 141

Calculating mean and sd of bedtime (hh:mm) in R - problem are times before/after midnight

I got the following dataset:

data <- read.table(text="
wake_time sleep_time
08:38:00  23:05:00  
09:30:00  00:50:00  
06:45:00  22:15:00  
07:27:00  23:34:00  
09:00:00  23:00:00  
09:05:00  00:10:00  
06:40:00  23:28:00  
10:00:00  23:30:00  
08:10:00  00:10:00  
08:07:00  00:38:00", header=T)

I used the chron-package to calculate the average wake_time:

> mean(times(data$wake_time))
[1] 08:20:12

But when I do the same for the variable sleep_time, this happens:

> mean(times(data$sleep_time))
[1] 14:04:00

I guess the result is distorted because the sleep_time contains times before and after midnight.

But how can I solve this problem?

Additionally: How can I calculate the sd of the times. I want to use it like "mean wake-up-time 08:20 ± 44 min" for example.

Upvotes: 2

Views: 512

Answers (1)

MrFlick
MrFlick

Reputation: 206187

THe times values are stored as numbers 0-1 representing a fraction of a day. If the sleep time is earlier than the wake time, you can "add a day" before taking the mean. For example

library(chron)
wake <- times(data$wake_time)
sleep <- times(data$sleep_time)
times(mean(ifelse(sleep < wake, sleep+1, sleep)))
# [1] 23:40:00

And since the values are parts of a day, if you want the sd in minutes, you'd take the partial day values and convert to minutes

sd(ifelse(sleep < wake, sleep+1, sleep) * 24*60)
# [1] 47.60252

Upvotes: 2

Related Questions