[GRASS-stats] Loading a point-vector table with 466 columns

[Nikos Alexandris]

Nikos:
> > # almost an hour...
> > Sys.time() ; sample_2 <- readVECT6("sample_2_grid_points") ; Sys.time()
> > [1] "2009-05-22 23:25:02 CEST"
> > OGR data source with driver: GRASS
> > Source:
> > "/geo/grassdb/peloponnese/evaluation_utm/nik/vector/sample_2_grid_points/head", layer: "1"
> > with  875  rows and  466  columns

> > Feature type: wkbPoint with 3 dimensions
> > [1] "2009-05-23 00:22:12 CEST"

Roger:
--%<---
> Does plugin=FALSE speed it up or slow it down (that would force the use of 
> a temporary shapefile)?

Yes, it speeds up.

# with "plugin=FALSE"
system.time(readVECT6("sample_2_grid_points", plugin=FALSE))
Exporting 875 points/lines...
 100%
875 features written
OGR data source with driver: ESRI Shapefile 
Source: "/geo/grassdb/peloponnese/evaluation_utm/nik/.tmp/vertical",
layer: "sample_2"
with  875  rows and  466  columns
Feature type: wkbPoint with 2 dimensions
   user  system elapsed 
169.450  24.677 204.882


## there is one difference: wkbPoint with "3" vs "2" dimensions ##
## what does this mean (wkbPoint)? OK, I look for it in the book ##


> > # while reading the csv...
> > Sys.time() ; sample_2 <-
> > read.csv(file="sample_2_grid_points_table.csv") ; Sys.time()
> > [1] "2009-05-23 01:39:51 CEST"
> > [1] "2009-05-23 01:39:52 CEST"

--%<---
> This is not a fair comparison, because you have to dump the CSV file from 
> the GRASS database first, although it won't take long. What are you using 
> to do that?

# right, it takes some time (<1min)
# running from within GRASS location
time db.out.ogr in=sample_2_grid_points
dsn=/geo/grassdb/peloponnese/R/R_files/sample_2_grid_points_table
format=CSV
Exported table
</geo/grassdb/peloponnese/R/R_files/sample_2_grid_points_table.csv>

real	0m46.845s
user	0m22.065s
sys	0m23.637s

> Have you considered connecting to the SQLite file directly 
> from R? Are the (2) coordinates present in the table? See:
> 
> http://cran.r-project.org/web/packages/RSQLite/index.html
> 
> for direct reading.

I was not aware of RSQLite. If it's straight-forward I'll try it today.
If you mean the x, y coordinates just as normal columns, no, I don't
require them currently.


Overview of loading grass attrubute table (875 rows, 466 colummns) via:

* readVECT6() with plugin=TRUE                         : ~57min
* readVECT6() with plugin=FALSE                        : ~3min+
* export from grass as CSV (~46sec) + read.csv (1 sec) : ~47sec

Nikos