Convert information from rows to new columns - r

Question

Is there a way in R to place every three values in the column "V" (below) to new columns? In others words, I need to reshape the data from long to wide, but only to three columns and where the values are what appears in column V. Below is a demonstration.
Thank you in advance!
data = structure(list(Key = c(200, 200, 200, 200, 200, 200, 300, 300,
300, 300, 300, 300, 400, 400, 400, 400, 400, 400),
V = c("a", "b", "c", "b", "d", "c", "d", "b", "c", "a", "f", "c", "d", "b",
"c", "a", "b", "c")),
row.names = c(NA, 18L),
class = "data.frame")

Answer 1

Here is one option
data %>%
group_by(Key) %>%
mutate(
grp = gl(n() / 3, 3),
col = c("x", "y", "z")[(row_number() + 2) %% 3 + 1]) %>%
group_by(Key, grp) %>%
spread(col, V) %>%
ungroup() %>%
select(-grp)
## A tibble: 6 x 4
# Key x y z
# <dbl> <chr> <chr> <chr>
#1 200 a b c
#2 200 b d c
#3 300 d b c
#4 300 a f c
#5 400 d b c
#6 400 a b c
Note: This assumes that the number of entries per Key is divisible by 3.
Instead of grp = gl(n() / 3, 3) you can also use grp = rep(1:(n() / 3), each = 3).
Update
In response to your comments, let's create sample data by removing some rows from data such that for Key = 200 and Key = 300 we don't have a multiple of 3 V entries.
data2 <- data %>% slice(-c(1, 8))
Then we can do
data2 %>%
group_by(Key) %>%
mutate(grp = gl(ceiling(n() / 3), 3)[1:n()]) %>%
group_by(Key, grp) %>%
mutate(col = c("x", "y", "z")[1:n()]) %>%
spread(col, V) %>%
ungroup() %>%
select(-grp)
## A tibble: 6 x 4
# Key x y z
# <dbl> <chr> <chr> <chr>
#1 200 b c b
#2 200 d c NA
#3 300 d c a
#4 300 f c NA
#5 400 d b c
#6 400 a b c
Note how "missing" values are filled with NA.