R: How to handle times without dates?
date, r, r-faq, time
Solution
Use the `"times"` class found in the chron package:
library(chron)
Enter <- c("09:12", "17:01")
Enter <- times(paste0(Enter, ":00"))
Exit <- c("10:15", "18:11")
Exit <- times(paste0(Exit, ":00"))
Exit - Enter # durations
sum(Enter < "10:00:00") # no entering before 10am
mean(Enter < "10:00:00") # fraction entering before 10am
sum(Exit > "17:00:00") # no exiting after 5pm
mean(Exit > "17:00:00") # fraction exiting after 5pm
table(cut(hours(Enter), breaks = c(0, 10, 17, 24))) # Counts for indicated hours
## (0,10] (10,17] (17,24]
## 1 1 0
table(hours(Enter)) # Counts of entries each hour
## 9 17
## 1 1
stem(hours(Enter), scale = 2)
## The decimal point is at the |
## 9 | 0
## 10 |
## 11 |
## 12 |
## 13 |
## 14 |
## 15 |
## 16 |
## 17 | 0
Graphics:
tab <- c(table(Enter), -table(Exit)) # Freq at each time. Enter is pos; Exit is neg.
plot(times(names(tab)), tab, type = "h", xlab = "Time", ylab = "Freq")
abline(v = c(10, 17)/24, col = "red", lty = 2) # vertical red lines
abline(h = 0) # X axis
Problem
I have data which includes `Date` as well as `Time enter` and `Time exit`. These latter two contain data like this: `08:02`, `12:02`, `23:45` etc. I would like to manipulate the `Time eXXX` data - for example, substract `Time enter` from `Time exit` to work out duration, or plot the distributions of `Time enter` and `Time exit`, e.g. to see if most entries are before 10:00, or if most exits are after 17:00. All the packages I've looked at require a date to precede the time, e.g. `01/02/2012 12:33`. Is this possible, or should I simply append an identical date to every time for the sake of calculations? This seem a bit messy!