rbind and spRbind
On Sun, 27 Jul 2008, Agustin Lobo wrote:
Acceptable, yes, but perhaps we should choose one or the other and, for sure, document the difference between spRbind and rbind. Personally, I find a bit odd spRbind() in that you get 2 variables that you were not seeing in data slot (I understand they are there as coordinates) of the original objects. This is not " rbind-like". But perhaps there are advantages that I'm not considering. Just wanted to point this out and make sure there were not other consequences at choosing between both functions.
rbind tries to be "like" rbind. Note that there is no default rbind generic method in base R - it is just a function. The original function is mean to join vectors and matrices by stacking them by row. It has no concept of anything other than the data. There are issues with stacking ordered objects by row, be they time series or whatever - so it isn't clear how this ought to be done. The rbind and spRbind methods for Spatial* objects try to help, but because user needs differ, no choices will meet all needs. As I said, the addition of the coordinates comes from the behaviour of the coercion method for SpatialPointsDataFrame to data.frame. There are no single good solutions here, perhaps other than dropping any similarity to the base rbind, IMHO. Roger
Also, sorry for not having included this info:
str(ika1v4geo)
Formal class 'SpatialPointsDataFrame' [package "sp"] with 5 slots ..@ data :'data.frame': 693 obs. of 23 variables: .. ..$ IKAPUNTO: int [1:693] 1 2 3 4 5 6 7 8 9 10 ... .. ..$ IKAID : num [1:693] 1 1 1 1 1 1 1 1 1 1 ... .. ..$ CN : chr [1:693] "Ivasichi" "Ivasichi" "Ivasichi" "Ivasichi" ... .. ..$ dia : chr [1:693] "2008-01-30" "2008-01-30" "2008-01-30" "2008-01-30" ... .. ..$ hora_obs: chr [1:693] " 8:48:21" " 8:55:17" " 9:00:22" " 9:07:13" ... .. ..$ GPSID : chr [1:693] "1-20080328-115" "1-20080328-116" "1-20080328-117" "1-20080328-118" ... .. ..$ GPS : int [1:693] 1 1 1 1 1 1 1 1 1 1 ... .. ..$ N_PUNTO : int [1:693] 115 116 117 118 119 120 122 123 124 125 ... .. ..$ GUIA : chr [1:693] "Endracio" "Endracio" "Endracio" "Endracio" ... .. ..$ MONITOR : chr [1:693] "Julio Vie" "Julio Vie" "Julio Vie" "Julio Vie" ... .. ..$ COD_SP_C: int [1:693] 29 9 10 29 8 8 28 8 28 29 ... .. ..$ SP_C : chr [1:693] "tatu" "jochi colorado" "jochi pintado" "tatu" ... .. ..$ COD_OBS : int [1:693] 5 5 5 5 6 6 6 7 6 8 ... .. ..$ OBS : chr [1:693] "huella" "huella" "huella" "huella" ... .. ..$ N : num [1:693] 1 1 1 1 1 1 1 1 1 1 ... .. ..$ VULN : int [1:693] 1 1 NA 1 3 3 NA 3 NA 1 ... .. ..$ VULNT : num [1:693] 1 1 NA 1 3 3 NA 3 NA 1 ... .. ..$ CL : num [1:693] 1 1 1 1 1 1 1 1 1 1 ... .. ..$ A : num [1:693] 8 8 8 8 8 8 8 8 8 8 ... .. ..$ H : num [1:693] 1.91 1.91 1.91 1.91 1.91 ... .. ..$ D : num [1:693] 0.719 0.719 0.719 0.719 0.719 ... .. ..$ S : num [1:693] 4 4 4 4 4 4 4 4 4 4 ... .. ..$ V : num [1:693] 34 34 34 34 34 34 34 34 34 34 ... ..@ coords.nrs : int [1:2] 8 9 ..@ coords : num [1:693, 1:2] 724547 724413 724367 724282 724225 ... .. ..- attr(*, "dimnames")=List of 2 .. .. ..$ : NULL .. .. ..$ : chr [1:2] "UTMX" "UTMY" ..@ bbox : num [1:2, 1:2] 716934 8303862 735638 8325272 .. ..- attr(*, "dimnames")=List of 2 .. .. ..$ : chr [1:2] "UTMX" "UTMY" .. .. ..$ : chr [1:2] "min" "max" ..@ proj4string:Formal class 'CRS' [package "sp"] with 1 slots .. .. ..@ projargs: chr NA Thanks! Agus Roger Bivand wrote:
On Sat, 26 Jul 2008, Danlin Yu wrote:
Agustin: Since you are using the sp method for binding, I suppose the coordinates (in UTM project according to the name) are added automatically (as the added two new names are UTMX and UTMY). Why not check these two values to see what's in them.
Yes, that's right. Your (cryptic) SPDF is a SpatialPointsDataFrame (could be Pixels or Polygons too ...), where the as(, "data.frame") coercion method adds back the columns "hidden" by the coordinates()<- assignment step earlier. spRbind uses the coercion method, rbind grabs the data slot with the @ operator. Both are acceptable. Roger
Hope this helps. Danlin Agustin Lobo wrote:
I'm a bit confused with the following: I have a SPDF object ika1v4
dim(ika1v4geo at data)
[1] 693 23
dim(ika1v4geo)
[1] 693 23 Then I do an rbind:
a <- rbind(ika1v4geo,ika1v4geo) dim(a)
[1] 1386 23
dim(a at data)
[1] 1386 23 But spRbind introduces 2 variables:
a2 <- spRbind(ika1v4geo,ika1v4geo) dim(a2)
[1] 1386 25
dim(a2 at data)
[1] 1386 25
names(a at data)
[1] "IKAPUNTO" "IKAID" "CN" "dia" "hora_obs" "GPSID" [7] "GPS" "N_PUNTO" "GUIA" "MONITOR" "COD_SP_C" "SP_C" [13] "COD_OBS" "OBS" "N" "VULN" "VULNT" "CL" [19] "A" "H" "D" "S" "V"
names(a2 at data)
[1] "IKAPUNTO" "IKAID" "CN" "dia" "hora_obs" "GPSID" [7] "GPS" "UTMX" "UTMY" "N_PUNTO" "GUIA" "MONITOR" [13] "COD_SP_C" "SP_C" "COD_OBS" "OBS" "N" "VULN" [19] "VULNT" "CL" "A" "H" "D" "S" [25] "V"
Why? Which are the differences between rbind and spRbind? Thanks! Agus
Roger Bivand Economic Geography Section, Department of Economics, Norwegian School of Economics and Business Administration, Helleveien 30, N-5045 Bergen, Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43 e-mail: Roger.Bivand at nhh.no