[GRASS-user] SQL: generating numeric class numbers from class text labels?

[Micha Silver]

How about doing this in R? The labels will be read into R as factors, 
and the factor levels can easily be extracted as numbers.

Something like this:


micha at tp480:~$ v.info -c stations
Displaying column types/names for database connection of layer <1>:
INTEGER|cat
INTEGER|station_num
TEXT|station_he
TEXT|station_en
TEXT|type
INTEGER|x_coord
INTEGER|y_coord
DOUBLE PRECISION|long
DOUBLE PRECISION|lat
INTEGER|elev
TEXT|date_open
DOUBLE PRECISION|dist
DOUBLE PRECISION|azim


micha at tp480:~$ R


R version 3.5.2 (2018-12-20) -- "Eggshell Igloo"
Copyright (C) 2018 The R Foundation for Statistical Computing
Platform: x86_64-pc-linux-gnu (64-bit)
.....

 > library(rgrass7)
Loading required package: XML
GRASS GIS interface loaded with GRASS version: GRASS 7.6.0 (2019)
and location: ITM
 > use_sf()
 > stations = readVECT("stations")
WARNING: Vector map <stations> is 3D. Use format specific layer creation
          options (parameter 'lco') to export <in 3D rather than 2D
          (default).
Exporting 94 features...
  100%
.....

 > stations['new_station_num'] = as.numeric(stations$station_en)
 > stations$new_station_num
  [1] 71 26  6 55 54 63  7  8 31 30 46 84 92 38 32 88 27 12 67 62 47 33 
53 76 89
[26]  2 86 11 40 65 64 45 13 85 60 59  1 74 73 22 19 15 39 50 56 14 44 
23 36 83
[51] 41 42 43 18 17 75 16 82 81 37 48 28 87  3 66 10 34 91 61 93 94 72  
5  4 68
[76] 78 77  9 29 51 58 57 49 52 24 25 80 79 35 70 69 90 21 20

 > writeVECT(SDF=stations, vname="new_stations")

Best regards, Micha


On 04/12/2019 19:11, Markus Neteler wrote:
> Hi,
>
> I have a landuse map with text labels (forest, street, ...). For
> r.learn.ml I need to have them as numeric classes.
> It is not important for me which number is assigned but I search for
> an automated solution, i.e. SQL statement unless there is a different
> way.
>
> So:
>
> cat|label|label_int
> 1|forest|1
> 2|forest|1
> 3|street|2
> 4|forest|1
> 5|street|2
> 6|urban|3
> ...
>
> I guess I have done that already some years ago but I can't remember
> the trick :-)
>
> thanks for a hint,
> Markus
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-- 
Micha Silver
Ben Gurion Univ.
Sde Boker, Remote Sensing Lab
cell: +972-523-665918
https://orcid.org/0000-0002-1128-1325