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Duncan Murdoch
On 05/02/2021 4:01 p.m., Christopher Carbone wrote:> Greetings,
>
> I found a bug in the cut.Date function of base R. My session info is
> at the bottom.
>
> The bug is in the "months" section of the code. Consider the
following:
>
> # Create vector with 365 days of year and cut into 12 months
> dates <-
seq(as.Date("2021-1-1"),as.Date("2021-12-31"),by="day")
> months <- cut(dates,"months",labels=1:12)
> table(months)
> # months
> # 1 2 3 4 5 6 7 8 9 10 11 12
> # 31 28 31 30 31 30 31 31 30 31 30 31
> # cut.Date works perfectly
>
> # Extend dates vector by adding following January and cut into 13 months
> dates <-
seq(as.Date("2021-1-1"),as.Date("2022-1-31"),by="day")
> months <- cut(dates,"months",labels=1:13)
> # Error in cut.default(unclass(x), unclass(breaks), labels = labels,
> right = right, :
> # lengths of 'breaks' and 'labels'
differ
> months <- cut(dates,"months",labels=1:14)
> table(months)
> # months
> # 1 2 3 4 5 6 7 8 9 10 11 12 13 14
> # 31 28 31 30 31 30 31 31 30 31 30 31 31 0
> # Bug: cut.Date adds a superfluous bin
> # This is because February has less than 31 days
> # Thus, the code adjusts the end into March instead of February
>
> Inspecting the source code, I see the problem resides in lines 31
> through 41, the section dealing with breaks="months":
>
> if (valid == 3L) {
> start$mday <- 1L
> start$isdst <- -1L
> end <- as.POSIXlt(max(x, na.rm = TRUE))
> step <- if (length(by2) == 2L)
> as.integer(by2[1L])
> else 1L
> 38 end <- as.POSIXlt(end + (31 * step * 86400))
> end$mday <- 1L
> end$isdst <- -1L
> breaks <- as.Date(seq(start, end, breaks))
>
> When the end is adjusted in line 38, there are instances where an
> unnecessary extra bin is created.
> This is accounted for in the breaks="quarters" case by testing at
the
> end and removing the final break if necessary.
> The same method employed here fixes the bug:
>
> if (valid == 3L) {
> start$mday <- 1L
> start$isdst <- -1L
> maxx <- max(x, na.rm = TRUE) # Added line
> end <- as.POSIXlt(maxx) # Modified line
> step <- if (length(by2) == 2L)
> as.integer(by2[1L])
> else 1L
> end <- as.POSIXlt(end + (31 * step * 86400))
> end$mday <- 1L
> end$isdst <- -1L
> breaks <- as.Date(seq(start, end, breaks))
> lb <- length(breaks) # Added line
> if (maxx < breaks[lb - 1]) # Added line
> breaks <- breaks[-lb] # Added line
>
> I modified cut.Date with the above code changes and stored it in a
> function called cut_Date():
>
> dates <-
seq(as.Date("2021-1-1"),as.Date("2022-1-31"),by="day")
> months <- cut_Date(dates,"months",labels=1:13)
> table(months)
> # months
> # 1 2 3 4 5 6 7 8 9 10 11 12 13
> # 31 28 31 30 31 30 31 31 30 31 30 31 31
>
> Thanks for your time and consideration!
>
>> sessionInfo()
> R version 4.0.3 (2020-10-10)
> Platform: x86_64-w64-mingw32/x64 (64-bit)
> Running under: Windows 10 x64 (build 19041)
>
> Matrix products: default
>
> locale:
> [1] LC_COLLATE=English_United States.1252 LC_CTYPE=English_United
States.1252
> [3] LC_MONETARY=English_United States.1252 LC_NUMERIC=C
> [5] LC_TIME=English_United States.1252
>
> attached base packages:
> [1] stats graphics grDevices utils datasets methods base
>
> loaded via a namespace (and not attached):
> [1] compiler_4.0.3 tools_4.0.3 tinytex_0.28 xfun_0.19
>
> Many Blessings,
> Christopher Carbone
>
> "Follow your bliss and doors will open where you didn't know they
were
> going to be..."
> -Joseph Campbell
>
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