[Rd] head.ts, tail.ts loses time

[Gabor Grothendieck]

It isn't really clear that it can't work.  This does work by inserting NA's.

  library(zoo)
  as.ts(as.zoo(lynx)[ c(1:3, 7) ] )
  ## Time Series:
  ## Start = 1821
  ## End = 1827
  ## Frequency = 1
  ## [1]  269  321  585   NA   NA   NA 3928


On Mon, Jun 10, 2024 at 10:32 AM Martin Maechler
<maechler using stat.math.ethz.ch> wrote:
>
> >>>>> Spencer Graves
> >>>>>     on Mon, 10 Jun 2024 07:50:13 -0500 writes:
>
>     > Hi, Gabor et al.: Thanks for this. I should change my
>     > current application to use either zoo or xts, as Gabor
>     > suggests.
>
>
>     >     However, I was surprised to learn that "[.ts" does NOT
>     > return an object of class "ts". I see that "head.default"
>     > and "head.matrix" both call "[", so "head" cannot return a
>     > ts object, because "[" doesn't.
>
> Yes, the default head() and tail() are built on  `[` very much
> on purpose.
> Note that   `[`  should *not* keep the "ts"  property  in
> general, e.g.,
>          lynx[c(1:3, 7)]
> cannot be a regular time series
>
> I think I'd consider using  windows() for a head.ts() and tail.ts(),
> but in any case, I am sympathetic adding such methods to "base R"'s
> utils package.
>
>
> Martin
>
>     >     Best Wishes, Spencer Graves
>
>
>     > On 6/9/24 8:40 PM, Gabor Grothendieck wrote:
>     >> zoo overcomes many of the limitations of ts:
>     >>
>     >> library(zoo) as.ts(head(as.zoo(presidents))) ## Qtr1 Qtr2
>     >> Qtr3 Qtr4 ## 1945 NA 87 82 75 ## 1946 63 50
>     >>
>     >> xts also works here.
>     >>
>     >> On Sun, Jun 9, 2024 at 12:04 PM Spencer Graves
>     >> <spencer.graves using prodsyse.com> wrote:
>     >>>
>     >>> Hello, All:
>     >>>
>     >>>
>     >>> The 'head' and 'tail' functions strip the time from a
>     >>> 'ts' object.  Example:
>     >>>
>     >>>
>     >>> > head(presidents) [1] NA 87 82 75 63 50
>     >>>
>     >>>
>     >>> > window(presidents, 1945, 1946.25) Qtr1 Qtr2 Qtr3 Qtr4
>     >>> 1945 NA 87 82 75 1946 63 50
>     >>>
>     >>>
>     >>> Below please find code for 'head.ts' and 'tail.ts' that
>     >>> matches 'window'.
>     >>>
>     >>>
>     >>> Comments?  Spencer Graves
>     >>>
>     >>> head.ts <- function(x, n=6L, ...){ tmx <-
>     >>> as.numeric(time(x))
>     >>> #
>     >>> utils:::checkHT(n, d <- dim(x)) if(is.na(n[1]) ||
>     >>> n[1]==0)ts(NULL)
>     >>> #
>     >>> firstn <- head(tmx, n[1]) if(is.null(d)){
>     >>> return(window(x, firstn[1], tail(firstn, 1))) } else{
>     >>> if(length(n)<2){ return(window(x, firstn[1],
>     >>> tail(firstn, 1))) } else { Cols <- head(1:d[2], n[2])
>     >>> xn2 <- x[, Cols[1]:tail(Cols, 1)] return(window(xn2,
>     >>> firstn[1], tail(firstn, 1))) } } }
>     >>>
>     >>>
>     >>> tail.ts <- function (x, n = 6L, ...)  {
>     >>> utils:::checkHT(n, d <- dim(x)) tmx <-
>     >>> as.numeric(time(x))
>     >>> #
>     >>> if(is.na(n[1]) || n[1]==0)ts(NULL)
>     >>> #
>     >>> lastn <- tail(tmx, n[1]) if(is.null(d)){
>     >>> return(window(x, lastn[1], tail(lastn, 1))) } else{
>     >>> if(length(n)<2){ return(window(x, lastn[1], tail(lastn,
>     >>> 1))) } else { Cols <- head(1:d[2], n[2]) xn2 <- x[,
>     >>> Cols[1]:tail(Cols, 1)] return(window(xn2, lastn[1],
>     >>> tail(lastn, 1))) } } }
>     >>>
>     >>>
>     >>> # examples head(presidents)
>     >>>
>     >>> head(presidents, 2)
>     >>>
>     >>> npresObs <- length(presidents) head(presidents,
>     >>> 6-npresObs)
>     >>>
>     >>> try(head(presidents, 1:2)) # 'try-error'
>     >>>
>     >>> try(head(presidents, 0)) # 'try-error'
>     >>>
>     >>> # matrix time series str(pres <-
>     >>> cbind(n=1:length(presidents), presidents)) head(pres, 2)
>     >>>
>     >>> head(pres, 2-npresObs)
>     >>>
>     >>> head(pres, 1:2) head(pres, 2:1) head(pres, 1:3)
>     >>>
>     >>> # examples tail(presidents)
>     >>>
>     >>> tail(presidents, 2)
>     >>>
>     >>> npresObs <- length(presidents) tail(presidents,
>     >>> 6-npresObs)
>     >>>
>     >>> try(tail(presidents, 1:2)) # 'try-error'
>     >>>
>     >>> try(tail(presidents, 0)) # 'try-error'
>     >>>
>     >>> # matrix time series str(pres <-
>     >>> cbind(n=1:length(presidents), presidents)) tail(pres, 2)
>     >>>
>     >>> tail(pres, 2-npresObs)
>     >>>
>     >>> tail(pres, 1:2) tail(pres, 2:1) tail(pres, 1:3)
>     >>>
>     >>> # for unit testing: headPres <- head(presidents) pres6
>     >>> <- ts(presidents[1:6], time(presidents)[1],
>     >>> frequency=frequency(presidents))
>     >>> stopifnot(all.equal(headPres, pres6))
>     >>>
>     >>> headPres2 <- head(presidents, 2) pres2 <-
>     >>> ts(presidents[1:2], time(presidents)[1],
>     >>> frequency=frequency(presidents))
>     >>> stopifnot(all.equal(headPres2, pres2))
>     >>>
>     >>> npresObs <- length(presidents) headPres. <-
>     >>> head(presidents, 6-npresObs)
>     >>> stopifnot(all.equal(headPres., pres6))
>     >>>
>     >>> headPresOops <- try(head(presidents, 1:2))
>     >>> stopifnot(class(headPresOops) == 'try-error')
>     >>>
>     >>> headPres0 <- try(head(presidents, 0))
>     >>> stopifnot(class(headPres0) == 'try-error')
>     >>>
>     >>> str(pres <- cbind(n=1:length(presidents), presidents))
>     >>> headP2 <- head(pres, 2)
>     >>>
>     >>> p2 <- ts(pres[1:2, ], time(presidents)[1],
>     >>> frequency=frequency(presidents))
>     >>> stopifnot(all.equal(headP2, p2))
>     >>>
>     >>> headP2. <- head(pres, 2-npresObs)
>     >>> stopifnot(all.equal(headP2., p2))
>     >>>
>     >>>
>     >>> #############
>     >>>
>     >>>
>     >>> sessionInfo() R version 4.4.0 (2024-04-24) Platform:
>     >>> aarch64-apple-darwin20 Running under: macOS Sonoma 14.5
>     >>>
>     >>> Matrix products: default BLAS:
>     >>> /System/Library/Frameworks/Accelerate.framework/Versions/A/Frameworks/vecLib.framework/Versions/A/libBLAS.dylib
>     >>>
>     >>> LAPACK:
>     >>> /Library/Frameworks/R.framework/Versions/4.4-arm64/Resources/lib/libRlapack.dylib;
>     >>> LAPACK version 3.12.0
>     >>>
>     >>> locale: [1]
>     >>> en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8
>     >>>
>     >>> time zone: America/Chicago tzcode source: internal
>     >>>
>     >>> attached base packages: [1] stats graphics grDevices
>     >>> utils datasets [6] methods base
>     >>>
>     >>> loaded via a namespace (and not attached): [1]
>     >>> compiler_4.4.0 tools_4.4.0
>     >>>
>     >>> ______________________________________________
>     >>> R-devel using r-project.org mailing list
>     >>> https://stat.ethz.ch/mailman/listinfo/r-devel
>     >>
>     >>
>     >>
>
>     > ______________________________________________
>     > R-devel using r-project.org mailing list
>     > https://stat.ethz.ch/mailman/listinfo/r-devel



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