R version 4.4.0 alpha (2024-04-02 r86304 ucrt)
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Platform: x86_64-w64-mingw32/x64

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> Sys.setenv(TZ="")
> suppressPackageStartupMessages(library(stars))
> matrix(1:4,2)
     [,1] [,2]
[1,]    1    3
[2,]    2    4
> m = matrix(1:4,2)
> s = st_as_stars(m)
> 
> s = st_set_dimensions(s, st_dimensions(s), xy = NULL) 
> sfc = st_sfc(st_point(0:1), st_point(3:2))
> s = st_set_dimensions(s, 1, sfc) |> st_set_crs(4326)
> tm = as.POSIXct("2023-03-04 12:35") + c(0, 3600)
> s = st_set_dimensions(s, 2, tm)
> f = tempfile(fileext = ".nc")
> write_mdim(s, f, as_float = FALSE)
Warning messages:
1: In CPL_write_mdim(file, driver, dimx, cdl, wkt, xy, root_group_options,  :
  GDAL Error 6: SetIndexingVariable() not implemented
2: In CPL_write_mdim(file, driver, dimx, cdl, wkt, xy, root_group_options,  :
  GDAL Error 6: SetIndexingVariable() not implemented
> s2 = read_mdim(f)
> #print(s2)
> print(all.equal(s, s2, check.attributes = FALSE))
[1] TRUE
> print(all.equal(s, s2))
[1] "Attributes: < Component \"dimensions\": Component \"X1\": Component \"refsys\": Component \"input\": 1 string mismatch >"                                   
[2] "Attributes: < Component \"dimensions\": Component \"X1\": Component \"refsys\": Component \"wkt\": 1 string mismatch >"                                     
[3] "Attributes: < Component \"dimensions\": Component \"X1\": Component \"values\": Attributes: < Component \"crs\": Component \"input\": 1 string mismatch > >"
[4] "Attributes: < Component \"dimensions\": Component \"X1\": Component \"values\": Attributes: < Component \"crs\": Component \"wkt\": 1 string mismatch > >"  
[5] "Attributes: < Component \"dimensions\": Component \"X2\": Component \"offset\": 'tzone' attributes are inconsistent ('' and 'UTC') >"                       
[6] "Attributes: < Component \"dimensions\": Component \"X2\": Component \"point\": 'is.NA' value mismatch: 1 in current 0 in target >"                          
> 
> st_crs(sfc) = st_crs(s2)
> st_crs(s) = st_crs(s2)
> tm = as.Date("2023-02-25") + 0:1
> sd = st_set_dimensions(s, 2, tm)
> print(sd)
stars object with 2 dimensions and 1 attribute
attribute(s):
    Min. 1st Qu. Median Mean 3rd Qu. Max.
A1     1    1.75    2.5  2.5    3.25    4
dimension(s):
   from to     offset  delta refsys point                   values
X1    1  2         NA     NA WGS 84  TRUE POINT (0 1), POINT (3 2)
X2    1  2 2023-02-25 1 days   Date FALSE                     NULL
> sd = st_set_dimensions(sd, 1, sfc)
> print(sd)
stars object with 2 dimensions and 1 attribute
attribute(s):
    Min. 1st Qu. Median Mean 3rd Qu. Max.
A1     1    1.75    2.5  2.5    3.25    4
dimension(s):
   from to     offset  delta refsys point                   values
X1    1  2         NA     NA WGS 84  TRUE POINT (0 1), POINT (3 2)
X2    1  2 2023-02-25 1 days   Date FALSE                     NULL
> f = tempfile(fileext = ".nc")
> write_mdim(sd, f)
Warning messages:
1: In CPL_write_mdim(file, driver, dimx, cdl, wkt, xy, root_group_options,  :
  GDAL Error 6: SetIndexingVariable() not implemented
2: In CPL_write_mdim(file, driver, dimx, cdl, wkt, xy, root_group_options,  :
  GDAL Error 6: SetIndexingVariable() not implemented
> sd2 = read_mdim(f)
> print(sd2)
stars object with 2 dimensions and 1 attribute
attribute(s):
    Min. 1st Qu. Median Mean 3rd Qu. Max.
A1     1    1.75    2.5  2.5    3.25    4
dimension(s):
   from to     offset  delta refsys point                   values
X1    1  2         NA     NA WGS 84  TRUE POINT (0 1), POINT (3 2)
X2    1  2 2023-02-25 1 days   Date    NA                     NULL
> print(all.equal(sd, sd2, check.attributes = FALSE))
[1] TRUE
> print(all.equal(sd, sd2))
[1] "Attributes: < Component \"dimensions\": Component \"X2\": Component \"point\": 'is.NA' value mismatch: 1 in current 0 in target >"
> # if (.Platform$OS.type == "unix") {
> #   print(read_mdim(paste0("/vsizip/", (system.file("zarr/sic_daily_sample.zarr.zip", package = "stars"))))
> # }
> 
> proc.time()
   user  system elapsed 
   0.64    0.14    0.78