R — Expand date range into panel data by group

Question

I have date ranges that are grouped by two variables (id and type) that are currently stored in a data frame called data. My goal is to ex

Answer 1

1) by Here is a three line answer using by from the base of R. First we convert the dates to "Date" class giving data2. Then we apply f which does the real work over each row and finally we rbind the resulting rows together:

data2 <- transform(data, from = as.Date(from), to = as.Date(to))

f <- function(x) with(x, data.frame(id, type, date = seq(from, to, by = "day")))
do.call("rbind", by(data, 1:nrow(data), f))

2) data.table Using the same data2 with data.table we do it like this:

library(data.table)

dt <- data.table(data2)
dt[, list(id, type, date = seq(from, to, by = "day")), by = 1:nrow(dt)]

2a) data.table or alternately this where dt is from (2) and f is from (1):

dt[, f(.SD), by = 1:nrow(dt)]

3) dplyr with dplyr it gives a warning but otherwise works where data2 and f are from (1):

data2 %>% rowwise() %>% do(f(.))

UPDATES Some improvements.

Answer 2

Here is one way to perform such a transformation using base functions

do.call(rbind,Map(function(id,type,from,to) {
    dts <- seq(from=from, to=to, by="1 day")
    dur <- length(dts)
    data.frame(
        id=rep(id, dur), 
        type=rep(type,dur),
        date=dts
    )
}, data$id, data$type, data$from, data$to))

And the first chunck of the output is

   id type                date
1   1    a 2009-02-21 02:00:00
2   1    a 2009-02-22 02:00:00
3   1    a 2009-02-23 02:00:00
4   1    a 2009-02-25 02:00:00
5   1    b 2009-02-25 02:00:00
6   1    b 2009-02-26 02:00:00
7   1    c 2009-02-26 02:00:00
8   1    c 2009-02-27 02:00:00
9   1    c 2009-02-28 02:00:00
10  1    c 2009-03-01 02:00:00
11  1    b 2009-02-26 02:00:00