如何在R中的data.frame中提取子序列的最后日期？

Question

I'm struggling for a while with the following dataset:

    id   date       var1 var2     
1   7031 2008-12-01  27  1
2   7031 2009-01-05   6  0
3   7031 2009-02-02   0  3
4   7031 2008-11-01   1  4
5   7500 2009-07-11  30  0
6   7500 2009-10-01   8  0
7   7500 2010-01-01   0  0
8   7041 2009-06-20  26  0
9   7041 2009-08-01   0  0
10  0277 2009-01-01   3  0

I would like to output for each id the last date with non-zero variables. Time series for these users are of different length. I expect as an output smth like:

id   last_date
7031 2009-02-02
7500 2009-10-01
7041 2009-06-20
0277 2009-01-01

Any help would be appreciated!

Answer 1

First, subset your data, and then use aggregate() :

Here's your sample data:

x <- read.table(header = TRUE, stringsAsFactors=FALSE, text = "
                id   date       var1 var2     
                1   '7031' 2008-12-01  27  1
                2   '7031' 2009-01-05   6  0
                3   '7031' 2009-02-02   0  3
                4   '7031' 2008-11-01   1  4
                5   '7500' 2009-07-11  30  0
                6   '7500' 2009-10-01   8  0
                7   '7500' 2010-01-01   0  0
                8   '7041' 2009-06-20  26  0
                9   '7041' 2009-08-01   0  0
                10  '0277' 2009-01-01   3  0")

Make sure that your "date" variable values are represented by actual dates and not characters.

x$date <- as.Date(x$date)

Subset:

x2 <- with(x, x[!(var1 == 0 & var2 == 0), ])

Aggregate:

aggregate(date ~ id, x2, max)
#     id       date
# 1  277 2009-01-01
# 2 7031 2009-02-02
# 3 7041 2009-06-20
# 4 7500 2009-10-01

If you didn't want to create a new object of your subsetted data, you can also use: aggregate(date ~ id, x[!(x$var1 == 0 & x$var2 == 0), ], max)