How to fill in every nth row and leave above rows with zero using dplyr?

Hi supposed I have a dataframe as such

temp <- data.frame(value = sample(c ( 1:312), 20 ), value2 = sample(c ( 1:312), 20 )  )

What I like to do is fill in every 3rd row with "hi" and leave the rest of the row above as either NA or 0. I tried doing this but

temp$t = "hi"

temp %>%
  mutate(
    prev = lag ( t, 3 )
  )

but this only works for the first 3 rows then everything is back is filled with "hi" What I want is to have "hi" only appear after every 3rd row. Ideally the first row should be "hi" as well.

thanks.

Solution

You may use rep -

temp$t <- rep(c('hi', NA, NA), length.out = nrow(temp))

If you prefer dplyr -

library(dplyr)

temp %>%
  mutate(t = rep(c('hi', NA, NA), length.out = n()))

#   value value2    t
#1     79    105   hi
#2    292    174 <NA>
#3     82     74 <NA>
#4    192    141   hi
#5    158    140 <NA>
#6    176    240 <NA>
#7      7     33   hi
#8     10    284 <NA>
#9     48    286 <NA>
#10    94    181   hi
#11   128     22 <NA>
#12    19    261 <NA>
#13   166    186   hi
#14   273     25 <NA>
#15   246    294 <NA>
#16   227    151   hi
#17   208    306 <NA>
#18   256    211 <NA>
#19   175    188   hi
#20   202     43 <NA>

This vector c('hi', NA, NA) is repeated until end of the data.