Extend an irregular sequence and add zeros to missing values

Question

I have a data frame with a sequence in \'col1\' and values in \'col2\':

col1 col2
2     0.02
5     0.12
9     0.91
13    1.13

I want to exp

Answer 1

Just for completeness, a self binary join using data.table (you will get NAs instead of zeroes, but that could be easily changed if needed)

library(data.table)
setDT(df)[.(seq(max(col1))), on = .(col1)]
#     col1 col2
#  1:    1   NA
#  2:    2 0.02
#  3:    3   NA
#  4:    4   NA
#  5:    5 0.12
#  6:    6   NA
#  7:    7   NA
#  8:    8   NA
#  9:    9 0.91
# 10:   10   NA
# 11:   11   NA
# 12:   12   NA
# 13:   13 1.13