6. How raster functions map to stars functions
Author: Sébastien Rochette, Adriano Fantini, Edzer Pebesma

# 6. How `raster` functions map to `stars` functions

#### Sébastien Rochette, Adriano Fantini, Edzer Pebesma

For a better version of the stars vignettes see https://r-spatial.github.io/stars/articles/

Here’s an attempt at the table describing how `raster` functions map to `stars` functions, discussed in issue #122. This table uses the functionality of the `raster` package as a template; it may be incomplete, imprecise or plain wrong, so take it with a pinch of salt. Any comment or correction is hugely appreciated, please contribute!

Some of the functions (`filter`, `slice`, `mutate`, `select`, `pull`, …) are provided via `dplyr`, which must be loaded. See `?stars::dplyr`.

## COMMENT LEGEND

? = Not sure / unknown

* = Not present, low priority

# = Not present, high priority

NA = Not available by design

## Creating objects

raster | stars | Note/comment
--- | --- | ---
{raster, stack, brick} (read) | read_stars or read_stars(along = …) |
{stack, brick} (concatenate layers) | c or c(along = …) |
subset | {[ ] , slice, filter} |
addLayer | c() or c(along = …) |
dropLayer | {[ ] , slice, filter} |
unstack | combine lapply and {[ ] , slice, filter} |

## Changing spatial extent and/or resolution of objects

raster | stars | Note/comment
--- | --- | ---
merge | c | #, currently only works for adjacent objects
mosaic | st_mosaic | these are not identical, read the docs carefully
crop | filter, st_crop |
setExtent |  | # maybe use st_warp?
trim |  | #
aggregate | aggregate | WIP; raster’s aggregate with fact=2 will not work, use st_warp in that case?
disaggregate |  | # use st_warp(use_gdal = TRUE)?
resample | {st_transform, st_warp} |
projectRaster | {st_transform, st_warp} |
shift |  | #, now use st_set_dimensions
flip | [] with reversed index | #
rotate |  | *
t |  | NA

## Cell based computation

raster | stars | Note/comment
--- | --- | ---
calc | st_apply |
overlay | c(along = , …) |> st_apply(…) |
cover | [ ] <- |
mask | [ ], st_crop | when using an sf polygon as mask
mask | [ ]<- NA | when using a stars object to mask
cut | cut |
subs |  |
reclassify | mutate with case_when | or forcats::fct_recode ?
reclassify | cut |
init | [ ] <- |
stackApply | {[ ] , slice, filter} |> st_apply(…) |
stackSelect |  |

## Spatial contextual computation

raster | stars | Note/comment
--- | --- | ---
distance |  | #
gridDistance |  | *
distanceFromPoints |  | #
direction |  | *
focal | f = st_apply(x1, 3, foc, w = matrix(1, 3, 3)) | See. issue 176
localFun |  | *
boundaries | st_as_sf(as_points=FALSE, merge=TRUE, connect8=TRUE) |
clump | st_as_sf(r, merge = TRUE) | `st_as_sf` returns polygons, `clump` a raster
adjacent |  | *
area | st_area |
terrain |  | #
Moran |  |

## Model predictions

raster | stars | Note/comment
--- | --- | ---
predict | predict |
interpolate | gstat::idw, gstat::krige | `st_warp` has raster-raster interpolations of `gdalwarp`

## Data type conversion

raster | stars | Note/comment
--- | --- | ---
rasterize | st_as_stars |
rasterToPoints | st_as_sf(as_points=TRUE) |
rasterToPolygons | st_as_sf(as_points=FALSE, …), st_polygonize |
rasterToContour | st_contour | requires GDAL >= 2.4.0
rasterFromXYZ |  |
rasterFromCells |  |

## Summarizing

raster | stars | Note/comment
--- | --- | ---
cellStats | st_apply |
summary | print, summary(as.vector(. |> pull())) |
freq | table | *
crosstab |  |
unique | unique(as.vector(. |> pull())) |
zonal |  | *

## Accessing values of objects

raster | stars | Note/comment
--- | --- | ---
getValues | {pull, [[ ]]} |
getValuesBlock | {[ ] , slice, filter} |> pull() |
getValuesFocal | {[ ] , slice, filter} |> pull() |
as.matrix | [[ ]] | currently behaves somewhat unexpectedly *
as.array | [[ ]] | currently behaves somewhat unexpectedly *
extract (by cell) | {[ ] , slice, filter} |
extract (by polygon) | x[sf_object] |
extract (by point) | aggregate(stars_object, sf_object, function(x) x[1], as_points = FALSE) |
sampleRandom |  | *
sampleRegular |  | *
minValue | purrr::map(x, min) |
maxValue | purrr::map(x, max) |
setMinMax |  | ,

## Plotting

raster | stars | Note/comment
--- | --- | ---
plot | plot, geom_stars |
plotRGB | plot(x, rgb =…) |
spplot | - |
image | image |
persp | - |
contour | (st_contour, then sf::plot) |
filledContour | (same) |
text | text |
`hist` | `hist(x[[1]])` |
barplot |  |
density |  |
pairs |  |
boxplot |  |

## Getting and setting dimensions

raster | stars | Note/comment
--- | --- | ---
ncol | dim(x)[1] | or use name instead of 1; cols may be the second dimension!
nrow | dim(x)[2] | or use name instead of 2; rows may be the first dimension!
ncell | prod(dim(x)) |
res | st_dimensions | can also not be a constant in case of rectilinear or curvilinear grids
nlayers | - | there is no concept of layers in stars
names | names |
xres | st_res(x)[1] | may not be a constant in case of rectilinear or curvilinear grids
yres | st_res(x)[2] | may not be a constant in case of rectilinear or curvilinear grids
xmin | st_bbox(x)[1] |
xmax | st_bbox(x)[3] |
ymin | st_bbox(x)[2] |
ymax | st_bbox(x)[4] |
extent | st_bbox(x) | different ordering of numbers
origin | - |
projection | st_crs(x) |
isLonLat | st_is_longlat(st_crs(x)) |
filename |  | stars_proxy objects carry file names where otherwise the array data is
bandnr |  | stars has no general concept of bands
nbands | dim(x)[3] | may also be time; bands may also be in another dimension, or have another name
compareRaster | all.equal(st_dimensions(x), st_dimensions(y)) | *
NAvalue |  | -

## Computing row, column, cell numbers and coordinates

raster | stars | Note/comment
--- | --- | ---
xFromCol | st_get_dimension_values(., ‘x’)[col] | I am not sure how to generally get the x dimension name - here it is x
yFromRow | st_get_dimension_values(., ‘y’)[row] | I am not sure how to generally get the y dimension name - here it is y
xFromCell |  |
yFromCell |  |
xyFromCell |  |
colFromX |  | *
rowFromY |  | *
rowColFromCell |  |
cellFromXY | st_cells() |
cellFromRowCol |  |
cellsFromExtent |  |
coordinates | st_coordinates |
validCell |  |
validCol | col |> between(st_dimensions(.)\(x\)from, st_dimensions(.)\(x\)to) | raster columns are not always named ‘x’
validRow | row |> between(st_dimensions(.)\(y\)from, st_dimensions(.)\(y\)to) | raster columns are not always named ‘y’
setValues | [ ] <- |
writeRaster | write_stars | currently uses GDAL, somewhat limited
KML |  |

The format of this table follows the `raster-package` entry in the raster manual, found at `https://cran.r-project.org/web/packages/raster/raster.pdf`.