Create a count-consecutive variable which resets to 1

Question

I have a dataset like the following, where \"group\" is a group variable. I want to count the number of \'next\' days by group, but if it is not the next day I want the count to

Answer 1

An option is to group by 'group', then use diff on the Date class convered 'date', create a logical vector and use cumsum to replicate the results in 'want' ('wantn') and then with the 'wantn', apply max on it

library(dplyr)
library(data.table)
df %>% 
   group_by(group) %>%
   mutate(wantn = rowid(cumsum(c(TRUE, diff(as.Date(date)) !=1))), 
          want2n = max(wantn))
# A tibble: 7 x 6
# Groups:   group [2]
#  group date        want want2 wantn want2n
#             
#1     1 2000-01-01     1     3     1      3
#2     1 2000-01-03     1     3     1      3
#3     1 2000-01-04     2     3     2      3
#4     1 2000-01-05     3     3     3      3
#5     2 2000-01-09     1     2     1      2
#6     2 2000-01-10     2     2     2      2
#7     2 2000-01-12     1     2     1      2

or if we want to not use rowid, then create the grouping variable with cumsum and get the sequence

df %>%
    group_by(group) %>%
    group_by(group2 = cumsum(c(TRUE, diff(as.Date(date)) !=1)), add = TRUE) %>%
    mutate(wantn = row_number()) %>%
    group_by(group) %>%
    mutate(want2n = max(wantn)) %>%       
    select(-group2)