r - How to number/label data-table by group-number from group_by? -

i have tbl_df want group_by(u,v) each distinct integer combination observed (u,v).

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edit: resolved adding group_indices() in dplyr 0.4.0

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a) want assign each distinct group arbitrary distinct number label=1,2,3... e.g. combination (u,v)==(2,3) label 1, (1,3) 2, , on. how 1 mutate(), without three-step summarize-and-self-join?

dplyr has neat function n(), gives number of elements within group, not overall number of group. in data.table called .grp.

b) want assign string/character label ('a','b',...). numbering groups integers good-enough, because can use integer_to_label(i) below. unless there's clever way merge these two? don't sweat part.

set.seed(1234)  # helper fn mapping integer 1..26 character label integer_to_label <- function(i) { substr("abcdefghijklmnopqrstuvwxyz",i,i) }  df <- tbl_df(data.frame(u=sample.int(3,10,replace=t), v=sample.int(4,10,replace=t)))  # want label/number each distinct group of unique (u,v) combinations df %>% group_by(u,v) %>% mutate(label = n()) # wrong: n() number of element within group, not overall number of group     u v 1  2 3 2  1 3 3  1 2 4  2 3 5  1 2 6  3 3 7  1 3 8  1 2 9  3 1 10 3 4  kludge 1: df %>% group_by(u,v) %>% summarize(label = n()) , self-join 

updated answer

get_group_number = function(){     = 0     function(){         <<- i+1             } } group_number = get_group_number() df %>% group_by(u,v) %>% mutate(label = group_number()) 

you can consider following unreadable version

group_number = (function(){i = 0; function() <<- i+1 })() df %>% group_by(u,v) %>% mutate(label = group_number()) 

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using iterators package

library(iterators)  counter = icount() df %>% group_by(u,v) %>% mutate(label = nextelem(counter))