Hi, 

I am quite new in R, but want to try the
following data aggregation in R. The data has
three columns, and the fourth is what i am trying
to get. I created this in SAS, and would like to
learn to do it in R.

Here is some snapshot of the dataset. I have a
list of different users, and on different dates
(sorted), they had played several rounds of
plays. Date here is coded ascendingly. On each
date per user, I want to sum the total number of
plays for a span of 3 days counting backward. For
example, on the date of 16528 for user 1, the
back3 should the sum of 9+3+8=20. For those dates
that can only go back for less than 3 days, sum
the number of plays on available dates. For
example, on date 16527 for userid 1, there are
only 2 days, so the sum is 3+8=11.

Userid  plays   date    back3
1       8       16526   8
1       3       16527   11
1       9       16528   20
1       4       16529   16
1       3       16531   16
1       12      16532   19
1       3       16533   18
1       16      16534   31
1       6       16535   25
1       16      16536   38
1       10      16537   32
2       30      16528   30
2       16      16529   46
2       15      16530   61
2       11      16531   42
2       9       16532   35
2       11      16533   31
2       24      16534   44
2       21      16535   56
2       37      16536   82
2       6       16537   64
2       58      16538   101
2       34      16539   98
2       19      16540   111
2       18      16541   71
2       23      16542   60
2       35      16543   76
2       10      16544   68
2       7       16545   52
2       1       16546   18
2       15      16547   23
2       10      16548   26
2       12      16549   37
2       20      16550   42
2       18      16551   50
2       12      16552   50
2       8       16553   38
2       8       16554   28
2       32      16555   48
2       12      16556   52
2       13      16557   57
2       25      16610   50
3       1       16574   1
3       1       16576   2
3       1       16577   3
3       1       16578   3
3       2       16587   4
3       2       16588   5
3       1       16590   5
3       4       16602   7
3       1       16603   6
3       1       16624   6
3       6       16625   8
3       3       16626   10
3       4       16653   13
3       3       16654   10

Any help is appreciated.
Alfred


 
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