[help] Name spec for vctrs::vec_c in dynamic target aggregation makes it impossible to aggregate st::sf objects

[guglicap]

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Description

Hello. In my project I'm using dynamic branching to process spatial data, and I'd like to aggregate the output. This should be done automatically by targets, but unfortunately at the moment this doesn't work because of the name specification for the vctrs::vec_c call, since it is being applied to sfc_* types, which do not implement vctrs methods. The offending line, in my specific case is this one. Here's a reprex demonstrating the behaviour, as you can see, removing the name spec makes the aggregation work again.

nc <- sf::st_read(system.file("shape/nc.shp", package="sf"))
#> Reading layer `nc' from data source `/home/goo/programming/R/libs/sf/shape/nc.shp' using driver `ESRI Shapefile'
#> Simple feature collection with 100 features and 14 fields
#> Geometry type: MULTIPOLYGON
#> Dimension:     XY
#> Bounding box:  xmin: -84.32385 ymin: 33.88199 xmax: -75.45698 ymax: 36.58965
#> Geodetic CRS:  NAD27
nc1 <- sf::st_read(system.file("shape/nc.shp", package="sf"))
#> Reading layer `nc' from data source `/home/goo/programming/R/libs/sf/shape/nc.shp' using driver `ESRI Shapefile'
#> Simple feature collection with 100 features and 14 fields
#> Geometry type: MULTIPOLYGON
#> Dimension:     XY
#> Bounding box:  xmin: -84.32385 ymin: 33.88199 xmax: -75.45698 ymax: 36.58965
#> Geodetic CRS:  NAD27

objs <- list(nc, nc1)
objs$.name_spec <- "{outer}_{inner}"
do.call(vctrs::vec_c, objs)
#> Error:
#> ! Can't use a name specification with non-vctrs types.
#> vctrs methods must be implemented for class `sfc_MULTIPOLYGON`.
#> See <https://vctrs.r-lib.org/articles/s3-vector.html>.

objs$.name_spec <- NULL
do.call(vctrs::vec_c, objs) |> head() # do not print 200 lines
#>    AREA PERIMETER CNTY_ CNTY_ID        NAME  FIPS FIPSNO CRESS_ID BIR74 SID74
#> 1 0.114     1.442  1825    1825        Ashe 37009  37009        5  1091     1
#> 2 0.061     1.231  1827    1827   Alleghany 37005  37005        3   487     0
#> 3 0.143     1.630  1828    1828       Surry 37171  37171       86  3188     5
#> 4 0.070     2.968  1831    1831   Currituck 37053  37053       27   508     1
#> 5 0.153     2.206  1832    1832 Northampton 37131  37131       66  1421     9
#> 6 0.097     1.670  1833    1833    Hertford 37091  37091       46  1452     7
#>   NWBIR74 BIR79 SID79 NWBIR79                       geometry
#> 1      10  1364     0      19 MULTIPOLYGON (((-81.47276 3...
#> 2      10   542     3      12 MULTIPOLYGON (((-81.23989 3...
#> 3     208  3616     6     260 MULTIPOLYGON (((-80.45634 3...
#> 4     123   830     2     145 MULTIPOLYGON (((-76.00897 3...
#> 5    1066  1606     3    1197 MULTIPOLYGON (((-77.21767 3...
#> 6     954  1838     5    1237 MULTIPOLYGON (((-76.74506 3...

^{Created on 2024-12-15 with reprex v2.1.1}
I'd like to know if there's any workaround, apart from using iteration = list and declaring another target to do the aggregation in some other way. Although, I do think my use case should be common enough to warrant a built-in solution
Thanks.

[wlandau]

This is tricky because targets tries to preserve the names of dynamic branches and .name_spec is required when aggregating true vectors with lengths > 1. d01f86d falls back on do.call(vctrs::vec_c, unname(objects)) with no name spec. I think this fixes the issue.