Why doesn't cellnumbers() preserve the order in the query object?

[CaptureOSM]

Hi,

I find cellnumbers() very very usefull!

Let me just point out a mistake I did in the begining, which might occur only in the case of points data. when you want to combine a column from the original spatial query with the output of cellnumbers() . Here is a reproducible example

library(sf)
library(tabularaster)  

# create some labeled data 
sq <- seq(0, 1, by = 0.1)
p <- st_as_sf(expand.grid(sq, sq), coords = c("Var1", "Var2"))
p$label <- rep(c("A", "B"), length.out = nrow(p))

# load raster data
r <- raster(volcano)

# extract volcano data and append labels (e.g. for descriptive stats or regression)
cn <- cellnumbers(r, p) %>% mutate(elev = extract(r, cell_),
                                   label = p$label) # and here is the mistake. It is very tempting to 
                                                             # to simply `cbind`

Simply cbinding the output of cellnumbers() back to the original spatial object (or transfering any extra columns from p to cn as I am showing here) is wrong because the order of p is not preserved in cn. The correct way would be to join by row_id

 cn <- cellnumbers(r, p) %>% mutate(elev = extract(r, cell_))
 p <- rowid_to_column(p) # additional step needed to create a join column 
 p <- left_join(p, cn, by = c('rowid' = 'object_'))

So i just wanted to point that. Or is there better way to perform this type of extraction followed by combination with original point data?

I see several ways to improve this

• order the output of cellnumbers() by object_.
• Maybe consider renaming object_ to rowid as semanticaly speaking they are the same.
• Or provide the option in cellnumbers call to select a column from the spatial object to become the object_ column.

[mdsumner]

eek, that's certainly not supposed to be like that ... I see other problems too, thanks for the report

[mdsumner]

could you check your workflow with latest commit?

02d998e

I need to submit soon to align to the new spatstat, so this fix can get on CRAN soon (thank you!)

[CaptureOSM]

It works, now the object_ is ordered and the output of join and cbind is the same.

cn <- 
      cellnumbers(r, p) %>% 
       mutate(elev = extract(r, cell_),
                    label = p$label)

p <- 
      rowid_to_column(p) %>% 
      left_join(cn, by = c('rowid' = 'object_'))

 sum(!(p$label.x == p$label.y))
 # 0

[mdsumner]

Thanks! Clearly I need some tests on this