group - Count unique data point in grouped data in R -


this question has answer here:

i've been searching hours on , cannot find solution.

i have below data set:

   id   rank      1   1            1   3            1   3            1   4            2   2            2   3            2   3            2   3            3   1            4   2            4   2

i'm trying group id , produce count of how many unique times rank shows within group id results 

   id   rank  unique     1   1       1     1   3       2     1   3       2     1   4       1     2   2       1     2   3       3     2   3       3     2   3       3     3   1       1     4   2       2     4   2       2

i'm using formula , it's providing result of in rank column 

unique <- with(data, rank, id, fun = function(i) length((unique(i))))

any extremely appreciated!

base r solution. tabulates number of items cross-classified id , rank. ave function useful when can identify 1 vector need f=unction applied within possibly multiple criteria need result distributed dataframe: length function doing counting:

> dat$unique <- with(dat, ave(id, id, rank, fun=length)) > dat    id rank unique 1   1    1      1 2   1    3      2 3   1    3      2 4   1    4      1 5   2    2      1 6   2    3      3 7   2    3      3 8   2    3      3 9   3    1      1 10  4    2      2 11  4    2      2

when @hadley decided redefine r in dplyr, used count name of equivalent function.


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