R- Calculate a count of items over time using start and end dates

Question

I want to calculate a count of items over time using their Start and End dates.

Some sample data

START <- as.Date(c(\"2014-01-01\", \"2014-01-02\         


        

Answer 1

Using dplyr and grouped data:

data_frame(
            START = as.Date(c("2014-01-01", "2014-01-02","2014-01-03","2014-01-03")),
            END   = as.Date(c("2014-01-04", "2014-01-03","2014-01-03","2014-01-04"))
           ) -> df
rbind(cbind(group = 'a', df),cbind(group = 'b', df)) %>% as_data_frame->df
df

df %>% 
  group_by(.,group) %>% 
  do(data.frame(table(Reduce(c, Map(seq, .$START, .$END, by = 1)))))

This is a common problem when you for example want to find the number of logins on different pages/machines etc given time-intervals per users

> df
Source: local data frame [8 x 3]

  group      START        END
  (chr)     (date)     (date)
1     a 2014-01-01 2014-01-04
2     a 2014-01-02 2014-01-03
3     a 2014-01-03 2014-01-03
4     a 2014-01-03 2014-01-04
5     b 2014-01-01 2014-01-04
6     b 2014-01-02 2014-01-03
7     b 2014-01-03 2014-01-03
8     b 2014-01-03 2014-01-04
> 
> df %>% 
+   group_by(.,group) %>% 
+   do(data.frame(table(Reduce(c, Map(seq, .$START, .$END, by = 1)))))
Source: local data frame [8 x 3]
Groups: group [2]

  group       Var1  Freq
  (chr)     (fctr) (int)
1     a 2014-01-01     1
2     a 2014-01-02     2
3     a 2014-01-03     4
4     a 2014-01-04     2
5     b 2014-01-01     1
6     b 2014-01-02     2
7     b 2014-01-03     4
8     b 2014-01-04     2