how to debug invalid subscript type 'integer' error in R -

i'm trying run code in r: extract maximum value in vector under conditions keep getting error

error in list(id.2 = c(3l, 3l, 3l, 3l, 3l, 3l, 3l, 3l, 3l, 3l, 3l, 3l,  :    invalid subscript type 'integer' 

the code following:

require(dplyr) dat <- read.table(header = true, text = "id    name    year    job    job2 cumu_job2 1   jane    1980    worker  0   0 1   jane    1981    manager 1   1 1   jane    1982    sales   0   0 1   jane    1983    sales   0   0 1   jane    1984    manager 1   1 1   jane    1985    manager 1   2 1   jane    1986    boss    0   0 2   bob     1985    worker  0   0 2   bob     1986    sales   0   0 2   bob     1987    manager 1   1 2   bob     1988    manager 1   2 2   bob     1989    boss    0   0 3   jill    1989    worker  0   0 3   jill    1990    boss    0   0")  dat %.%   group_by(id) %.%   mutate(     all_jobs = sum(unique(job) %in% c("sales","manager","boss")),     cumu_max = max(cumu_job2)   ) %.%   filter(all_jobs == 3, job %in% c("sales","boss"))  source: local data frame [5 x 8] groups: id    id name year   job job2 cumu_job2 all_jobs cumu_max 1  1 jane 1982 sales    0         0        3        2 2  1 jane 1983 sales    0         0        3        2 3  1 jane 1986  boss    0         0        3        2 4  2  bob 1986 sales    0         0        3        2 5  2  bob 1989  boss    0         0        3        2 

the sample code works me, too. have found can repro similar error if attempt this:

dat %.%  group_by(dat$id) %.%  mutate(      all_jobs = sum(unique(job) %in% c("sales","manager","boss")),      cumu_max = max(cumu_job2)  ) %.%  filter(all_jobs == 3, job %in% c("sales","boss")) 

that is, if type "group_by(dat$id)" instead of "group_by(id)"