Creating dataframe rows with timestamp increments - r

Question

I have a dataframe with a structure similar to this:
name
time_from
time_to
value
a
2020-01-01 00:00:00
2020-01-01 01:30:00
value1
a
2020-01-01 02:00:00
2020-01-01 02:30:00
value2
b
2020-01-01 00:00:00
2020-01-01 01:00:00
value3
I want to convert the dataframe to the following structure by increasing the time_from timestamp by 30 minutes up to the time_to timestamp value while the name and value remain the same over the timestamp increments.
name
time
value
a
2020-01-01 00:00:00
value1
a
2020-01-01 00:30:00
value1
a
2020-01-01 01:00:00
value1
a
2020-01-01 01:30:00
value1
a
2020-01-01 02:00:00
value2
a
2020-01-01 02:30:00
value2
b
2020-01-01 00:00:00
value3
b
2020-01-01 00:30:00
value3
b
2020-01-01 01:00:00
value3
Help and guidance would be greatly appreciated. Thank you.

Answer 1

Using seqPOSIXt in a by approach.
dat <- do.call(rbind, by(dat, dat[c('name', 'value')], function(x) {
setNames(
data.frame(x[1, 1], seq.POSIXt(x[1, 2], x[nrow(x), 3], by='30 min'), x[1, 4]),
c('name', 'time', 'value'))}))
dat
# name time value
# 1 a 2020-01-01 00:00:00 value1
# 2 a 2020-01-01 00:30:00 value1
# 3 a 2020-01-01 01:00:00 value1
# 4 a 2020-01-01 01:30:00 value1
# 5 a 2020-01-01 02:00:00 value2
# 6 a 2020-01-01 02:30:00 value2
# 7 b 2020-01-01 00:00:00 value3
# 8 b 2020-01-01 00:30:00 value3
# 9 b 2020-01-01 01:00:00 value3
Of course, the solution assumes correctly formated 'POSIXct' format as input. Convert beforehand if you don't have it:
tcols <- c('time_from', 'time_to')
dat[tcols] <- lapply(dat[tcols], as.POSIXct)
Data:
dat <- structure(list(name = c("a", "a", "b"), time_from = structure(c(1577833200,
1577840400, 1577833200), class = c("POSIXct", "POSIXt"), tzone = ""),
time_to = structure(c(1577838600, 1577842200, 1577836800), class = c("POSIXct",
"POSIXt"), tzone = ""), value = c("value1", "value2", "value3"
)), row.names = c(NA, -3L), class = "data.frame")