[R-sig-Geo] Help to improve a code to substract two columns, delete and save shape-file

[Paul Hiemstra]

Ale,

Some remarks between the lines:

Alessandro schreef:
>
> Thanks for All help give me.
>
> I spoke with my professor and now I must do some changes. After 
> subtract the column Z with clomun DEM_SGRD to obtain column H. I wish 
> to create a new shape with only this H column. I tried and tried but 
> when I write the shape file there is always an error.
>
> Sorry for all disturb.
>
> I don’t want to be ill-mannered, to use improperly your time, but 
> before to save the shape is It possible to save only all records with 
> H value > of 2. (the statistical analysis need this clean)
>
> Thanks
>
> Ale
>
> > prova <- readOGR(".", "prova")
>
> OGR data source with driver: ESRI Shapefile
>
> Source: ".", layer: "prova"
>
> with 42 rows and 2 columns
>
> > summary(prova)
>
> Object of class SpatialPointsDataFrame
>
> Coordinates:
>
> min max
>
> coords.x1 267980.1 267998.1
>
> coords.x2 4147799.4 4147818.8
>
> Is projected: NA
>
> proj4string : [NA]
>
> Number of points: 42
>
> Data attributes:
>
> Z DEM_SGRD
>
> Min. :1415 Min. :1412
>
> 1st Qu.:1419 1st Qu.:1413
>
> Median :1421 Median :1414
>
> Mean :1423 Mean :1414
>
> 3rd Qu.:1424 3rd Qu.:1415
>
> Max. :1437 Max. :1417
>
> > prova$H <- prova$Z - prova$DEM_SGRD
>
> > summary(prova)
>
> Object of class SpatialPointsDataFrame
>
> Coordinates:
>
> min max
>
> coords.x1 267980.1 267998.1
>
> coords.x2 4147799.4 4147818.8
>
> Is projected: NA
>
> proj4string : [NA]
>
> Number of points: 42
>
> Data attributes:
>
> Z DEM_SGRD H
>
> Min. :1415 Min. :1412 Min. : 3.169
>
> 1st Qu.:1419 1st Qu.:1413 1st Qu.: 5.612
>
> Median :1421 Median :1414 Median : 7.320
>
> Mean :1423 Mean :1414 Mean : 9.265
>
> 3rd Qu.:1424 3rd Qu.:1415 3rd Qu.:10.982
>
> Max. :1437 Max. :1417 Max. :21.806
>
> > prova2 <- prova$H
>
Here you extract the data from prova, not including the coordinates. 
Look at class(prova2) to see that it is no longer a 
SpatialPointsDataFrame but a data.frame. Use the following syntax to get 
the data plus the coordinates:

prova2 <- prova["H"]

Now you can export it using write OGR. To get only the values above H == 2:

prova_Hgt2 = prova2[prova2$H > 2,]

Or combining the two actions above into one command:

prova2 = prova[prova$H > 2, "H"]

cheers,
Paul
>
> > summary(prova2)
>
> Min. 1st Qu. Median Mean 3rd Qu. Max.
>
> 3.169 5.612 7.320 9.265 10.980 21.810
>
> > writeOGR(prova2, ".", "prova2", driver="ESRI Shapefile")
>
> Errore in writeOGR(prova2, ".", "prova2", driver = "ESRI Shapefile") :
>
> obj of wrong class
>
> ------------------------------------------------------------------------
>
> _______________________________________________
> R-sig-Geo mailing list
> R-sig-Geo at stat.math.ethz.ch
> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>   


-- 
Drs. Paul Hiemstra
Department of Physical Geography
Faculty of Geosciences
University of Utrecht
Heidelberglaan 2
P.O. Box 80.115
3508 TC Utrecht
Phone:  +3130 274 3113 Mon-Tue
Phone:  +3130 253 5773 Wed-Fri
http://intamap.geo.uu.nl/~paul