在下面的示例中，我使用 st_apply() 扫描 x 的空间维度并返回与 band 对应的向量维度，产生星星对象y。由于 x 和 y 原则上是相同的，因此减去两者应该得到一个用零填充的星星对象。正如您在第二张图片中看到的那样，这不起作用。
问题在于尺寸已重新排列。如何重新排列它们以便 x-y 正常工作？
标记
PS这是一个相当人为的示例，但它源于一个在非空间维度上平滑的现实世界示例。
library(stars)
#> Loading required package: abind
#> Loading required package: sf
#> Linking to GEOS 3.8.0, GDAL 3.0.4, PROJ 6.3.1; sf_use_s2() is TRUE
#> Registered S3 methods overwritten by 'stars':
#> method from
#> st_bbox.SpatRaster sf
#> st_crs.SpatRaster sf
tif <- system.file("tif/L7_ETMs.tif", package = "stars")
x <- read_stars(tif)
x
#> stars object with 3 dimensions and 1 attribute
#> attribute(s):
#> Min. 1st Qu. Median Mean 3rd Qu. Max.
#> L7_ETMs.tif 1 54 69 68.91242 86 255
#> dimension(s):
#> from to offset delta refsys point values x/y
#> x 1 349 288776 28.5 UTM Zone 25, Southern Hem... FALSE NULL [x]
#> y 1 352 9120761 -28.5 UTM Zone 25, Southern Hem... FALSE NULL [y]
#> band 1 6 NA NA NA NA NULL
plot(x)
#> downsample set to c(1,1,1)
y <- st_apply(x,c("x","y"),FUN=function(x) x)
y
#> stars object with 3 dimensions and 1 attribute
#> attribute(s):
#> Min. 1st Qu. Median Mean 3rd Qu. Max.
#> L7_ETMs.tif 1 54 69 68.91242 86 255
#> dimension(s):
#> from to offset delta refsys point values
#> function(x) x 1 6 NA NA NA NA NULL
#> x 1 349 288776 28.5 UTM Zone 25, Southern Hem... FALSE NULL
#> y 1 352 9120761 -28.5 UTM Zone 25, Southern Hem... FALSE NULL
#> x/y
#> function(x) x
#> x [x]
#> y [y]
d <- x-y
plot(d)
#> downsample set to c(1,1,1)
由 reprex package 于 2022 年 2 月 2 日创建(v2.0.1)
session 信息sessioninfo::session_info()
#> ─ Session info ───────────────────────────────────────────────────────────────
#> setting value
#> version R version 3.6.3 (2020-02-29)
#> os Ubuntu 20.04.3 LTS
#> system x86_64, linux-gnu
#> ui X11
#> language (EN)
#> collate en_US.UTF-8
#> ctype en_US.UTF-8
#> tz Etc/UTC
#> date 2022-02-02
#>
#> ─ Packages ───────────────────────────────────────────────────────────────────
#> package * version date lib source
#> abind * 1.4-5 2016-07-21 [1] CRAN (R 3.6.3)
#> assertthat 0.2.1 2019-03-21 [1] CRAN (R 3.6.3)
#> class 7.3-15 2019-01-01 [4] CRAN (R 3.5.2)
#> classInt 0.4-3 2020-04-07 [1] CRAN (R 3.6.3)
#> cli 3.1.0 2021-10-27 [1] CRAN (R 3.6.3)
#> crayon 1.4.2 2021-10-29 [1] CRAN (R 3.6.3)
#> curl 4.3.2 2021-06-23 [1] CRAN (R 3.6.3)
#> DBI 1.1.2 2021-12-20 [1] CRAN (R 3.6.3)
#> digest 0.6.29 2021-12-01 [1] CRAN (R 3.6.3)
#> dplyr 1.0.7 2021-06-18 [1] CRAN (R 3.6.3)
#> e1071 1.7-9 2021-09-16 [1] CRAN (R 3.6.3)
#> ellipsis 0.3.2 2021-04-29 [1] CRAN (R 3.6.3)
#> evaluate 0.14 2019-05-28 [1] CRAN (R 3.6.3)
#> fansi 1.0.0 2022-01-10 [1] CRAN (R 3.6.3)
#> fs 1.5.0 2020-07-31 [1] CRAN (R 3.6.3)
#> generics 0.1.0 2020-10-31 [1] CRAN (R 3.6.3)
#> glue 1.6.0 2021-12-17 [1] CRAN (R 3.6.3)
#> highr 0.9 2021-04-16 [1] CRAN (R 3.6.3)
#> htmltools 0.5.1.1 2021-01-22 [1] CRAN (R 3.6.3)
#> httr 1.4.2 2020-07-20 [1] CRAN (R 3.6.3)
#> KernSmooth 2.23-16 2019-10-15 [4] CRAN (R 3.6.1)
#> knitr 1.33 2021-04-24 [1] CRAN (R 3.6.3)
#> lifecycle 1.0.1 2021-09-24 [1] CRAN (R 3.6.3)
#> lwgeom 0.2-8 2021-10-06 [1] CRAN (R 3.6.3)
#> magrittr 2.0.1 2020-11-17 [1] CRAN (R 3.6.3)
#> mime 0.11 2021-06-23 [1] CRAN (R 3.6.3)
#> pillar 1.6.4 2021-10-18 [1] CRAN (R 3.6.3)
#> pkgconfig 2.0.3 2019-09-22 [1] CRAN (R 3.6.3)
#> proxy 0.4-26 2021-06-07 [1] CRAN (R 3.6.3)
#> purrr 0.3.4 2020-04-17 [1] CRAN (R 3.6.3)
#> R6 2.5.1 2021-08-19 [1] CRAN (R 3.6.3)
#> Rcpp 1.0.7 2021-07-07 [1] CRAN (R 3.6.3)
#> reprex 2.0.1 2021-08-05 [1] CRAN (R 3.6.3)
#> rlang 0.4.12 2021-10-18 [1] CRAN (R 3.6.3)
#> rmarkdown 2.10 2021-08-06 [1] CRAN (R 3.6.3)
#> rstudioapi 0.13 2020-11-12 [1] CRAN (R 3.6.3)
#> sessioninfo 1.1.1 2018-11-05 [1] CRAN (R 3.6.3)
#> sf * 1.0-5 2021-12-17 [1] CRAN (R 3.6.3)
#> stars * 0.5-3 2021-06-08 [1] CRAN (R 3.6.3)
#> stringi 1.7.3 2021-07-16 [1] CRAN (R 3.6.3)
#> stringr 1.4.0 2019-02-10 [1] CRAN (R 3.6.3)
#> tibble 3.1.6 2021-11-07 [1] CRAN (R 3.6.3)
#> tidyselect 1.1.1 2021-04-30 [1] CRAN (R 3.6.3)
#> units 0.7-2 2021-06-08 [1] CRAN (R 3.6.3)
#> utf8 1.2.2 2021-07-24 [1] CRAN (R 3.6.3)
#> vctrs 0.3.8 2021-04-29 [1] CRAN (R 3.6.3)
#> withr 2.4.3 2021-11-30 [1] CRAN (R 3.6.3)
#> xfun 0.25 2021-08-06 [1] CRAN (R 3.6.3)
#> xml2 1.3.2 2020-04-23 [1] CRAN (R 3.6.3)
#> yaml 2.2.1 2020-02-01 [1] CRAN (R 3.6.3)
#>
#> [1] /home/mapa/R/x86_64-pc-linux-gnu-library/3.6
#> [2] /usr/local/lib/R/site-library
#> [3] /usr/lib/R/site-library
#> [4] /usr/lib/R/library
最佳答案
我发现的一个解决方案是在进行算术运算之前使用 aperm() 重新排列 y 中的维度顺序:
library(stars)
#> Loading required package: abind
#> Loading required package: sf
#> Linking to GEOS 3.8.0, GDAL 3.0.4, PROJ 6.3.1; sf_use_s2() is TRUE
#> Registered S3 methods overwritten by 'stars':
#> method from
#> st_bbox.SpatRaster sf
#> st_crs.SpatRaster sf
tif <- system.file("tif/L7_ETMs.tif", package = "stars")
x <- read_stars(tif)
y <- st_apply(x,c("x","y"),FUN=function(x) x)
y <- aperm(y,c(2,3,1))
d <- x-y
d
#> stars object with 3 dimensions and 1 attribute
#> attribute(s):
#> Min. 1st Qu. Median Mean 3rd Qu. Max.
#> L7_ETMs.tif 0 0 0 0 0 0
#> dimension(s):
#> from to offset delta refsys point values x/y
#> x 1 349 288776 28.5 UTM Zone 25, Southern Hem... FALSE NULL [x]
#> y 1 352 9120761 -28.5 UTM Zone 25, Southern Hem... FALSE NULL [y]
#> band 1 6 NA NA NA NA NULL
plot(d)
#> Warning in plot.stars(d): breaks="quantile" leads to a single class; maybe try
#> breaks="equal" instead?
#> downsample set to c(1,1,1)
由 reprex package 于 2022 年 2 月 3 日创建(v2.0.1)
关于r - st_apply 的输出需要重新洗牌，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/70959666/