Ungroup after grouping by just one variable in dplyr

Question

I have a lot of units that are measured repeated times.

>df
Item value  year
1     20     1990
1     20     1991
2     30     1990
2     15     1990
2     5      1991
3     10     1991
4     15     1990
5     10     1991
5      5     1991

I am trying to use dplyr to remove values that have a low number of observations. On this toy data, lets say that I want to remove data which has fewer than 2 counts.

>df <- df %>% 
  group_by(Item) %>% 
  tally() %>% 
  filter(n>1)

Item  n
1     2
2     3
5     2

The problem is that I would like to expand this back to what it was, but with this filter. I attempted using the ungroup command, but that seems to only have an effect when grouping by two variables. How can I filter by item counts then get my original variables back i.e value and year. It should look like this:

>df
Item value  year
1     20     1990
1     20     1991
2     30     1990
2     15     1990
2     5      1991
5     10     1991
5      5     1991

Answer 1

More simply, use dplyr's row_number()

library(dplyr)

df <- read.table("clipboard", header = TRUE, stringsAsFactors = FALSE)

df %>% 
  group_by(Item) %>% 
  filter(max(row_number()) > 1) %>%
  ungroup()

# A tibble: 7 x 3
# Groups:   Item [3]
   Item value  year
  <int> <int> <int>
1     1    20  1990
2     1    20  1991
3     2    30  1990
4     2    15  1990
5     2     5  1991
6     5    10  1991
7     5     5  1991