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

This would do it. You can change the column names as necessary.

as.data.frame(table(Reduce(c, Map(seq, df$START, df$END, by = 1))))
#         Var1 Freq
# 1 2014-01-01    1
# 2 2014-01-02    2
# 3 2014-01-03    4
# 4 2014-01-04    2

As noted in the comments, Var1 in the above solution is now a factor, and not a date. To keep the date class in the first column, you could do some more work to the above solution, or use plyr::count instead of as.data.frame(table(...))

library(plyr)
count(Reduce(c, Map(seq, df$START, df$END, by = 1)))
#            x freq
# 1 2014-01-01    1
# 2 2014-01-02    2
# 3 2014-01-03    4
# 4 2014-01-04    2