Counts for time intervals

Question

I am building something based upon this helpful post. I have three related questions for the dataset `df`: ``` machine ISOdatetime 1 M1 2013-08-21 18:16:39 2 M1 2013-08-21 18:20:44 3 M1 2013-08-21 18:21:42 4 M1 2013-08-21 18:46:09 5 M1 2013-08-21 18:46:27 6 M1 2013-08-21 19:01:13 etc ``` I want figure out how many values occur within half-hourly periods and put in a new dataframe, like so: ``` machine ISOdatetime numberobs 1 M1 2013-08-21 18:30:00 3 2 M1 2013-08-21 19:00:00 2 3 M1 2013-08-21 19:30:00 1 etc ``` The following code of course works nicely for neat hourly lengths: `df2 <- data.frame(table(cut(df$ISOdatetime, breaks="hour")))` The following code counts in 30 min blocks, but does not start neatly at hourly/half hourly points (it takes the starting point from the first listed time, which is 18:16:39 and designates start as 18:16:00): `df2 <-data.frame(table(cut(df$ISOdatetime, breaks = "30 mins")))` Question 1. What might be an elegant fix? Should I specify the required inter…

Accepted Answer

You can use the `lubridate` package to extract the hour, minutes, etc. from a date object. If you know the minute of the event time, you know in which half hour the event toke place. I sampled some data with two machines. I added a variable of the "whole" half hour after which the event toke place, then you can just count these. Hope this is what you are after, good luck.

```
require(lubridate)
set.seed(1234)
example.dat <- data.frame(
  machine = paste("M", sample(1:2, 100, replace = T), sep = ""),
  dates = sort(as.POSIXct(sample(1377100000:1377110000, 100), origin = "1960-01-01"))
  )
example.dat <- example.dat[order(example.dat$machine), ]

halfHours <- ifelse(minute(example.dat$dates) < 30, 0, 30)
example.dat$datesHH <- example.dat$dates
minute(example.dat$datesHH) <- halfHours; second(example.dat$datesHH) <- 0

data.frame(table(example.dat[ ,c(1,3)]))
```

Counts for time intervals

Solution

Problem

Related problems