r - How to store index values using dplyr function -

the data (dat) have collected has 2 different buckets part of same set ("set") filled random number of marbles ("marbles") there 2 treatments, "color" (blue/white) , "size" (small/large). each trial done in different "blocks" (ie. time slot). 2 buckets part of 1 set. position of buckets noted ("position"). here sample of data.

colour set size    position  marbles block blue     1   small  1         8     1 blue     1   small  2         81    1 blue     6   small  1         14    2 blue     6   small  2         11    2 blue     1   large  4         0     1 blue     1   large  5         0     1 blue     1   large  1         3     1 blue     1   large  2         43    1 white    1   small  1         8     1 white    1   small  2         81    1 white    1   small  6         7     1 white    6   small  3         12    2 white    6   small  4         25    2 white    2   large  1         86    1 white    2   large  2         77    1 white    1   large  1         3     11 white    1   large  2         43    11 

for each unique replicate (i.e. unique combination of color, set, block, size), want find index position of max value of marbles.

library(dplyr) library(plyr) <- vector() result <- dat %>%    mutate(maxmarbles = max(dat$marbles)) %>%    group_by(colour, size, block, set) %>%    pos1 <- which(a == max(dat$marbles)) 

i keep running error says not find "%>%". verified installation of dplyr , ensured called library. however, unable detect problem , wondering perhaps syntax error i'm unable catch?

first rule: never ever load plyr after dplyr :)

now question. indices of rows have maximum number of marbles within group:

library(dplyr) result_df <- dat %>%    group_by(colour, size, block, set) %>%   mutate(result = (marbles == max(marbles))) result_vec <- which(result_df$result) 

if want boolean indices can omit which().