R, DataFrame - group by multiple rows -

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i have data.frame posts looks this:

 post_id   group_id hour(when posted) likes  1         1        13                  5  2         1        13                  6  3         1        23                  3  4         2        12                  30  5         2        13                  34  6         2        22                  10

i want plot likes distribution hours in each group, need data.frame one:

          0 ... 12 13 ... 22 23   <- hours gorup#1         0  11         3   <- sum of likes in group#i in xx hour group#2         30 34     10  0

how can group post group , hour?

assuming data.frame called "mydf", perhaps can try xtabs (since you're looking sum):

> xtabs(likes ~ group_id + hour, mydf)         hour group_id 12 13 22 23        1  0 11  0  3        2 30 34 10  0

to levels "hour", if sum "0" groups, factor "hour" column first.

another convenient alternative use dcast "reshape2" package.


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