ptt-r-20220721

library(data.table)

df <- data.table(hour = 1:24,
                 RH = c(sample(50:80, 20, replace = T), rep(NA, 4)))

df$RH <- sample(df$RH)

df[, RH03 := shift(RH, n=3L, fill=0, type="lag")]

df
#>      hour    RH  RH03
#>     <int> <int> <int>
#>  1:     1    NA     0
#>  2:     2    50     0
#>  3:     3    71     0
#>  4:     4    68    NA
#>  5:     5    54    50
#>  6:     6    76    71
#>  7:     7    NA    68
#>  8:     8    66    54
#>  9:     9    64    76
#> 10:    10    63    NA
#> 11:    11    51    66
#> 12:    12    69    64
#> 13:    13    80    63
#> 14:    14    70    51
#> 15:    15    58    69
#> 16:    16    60    80
#> 17:    17    74    70
#> 18:    18    NA    58
#> 19:    19    65    60
#> 20:    20    79    74
#> 21:    21    64    NA
#> 22:    22    62    65
#> 23:    23    NA    79
#> 24:    24    71    64
#>      hour    RH  RH03