[R-sig-Geo] How to delete some polygons from 'SpatialPolygonsDataFrame'

[Roland Harhoff]

Dear Fred,
you may try
mySpPolygonsDf[i, j]
with i the desired rows / polygons and j (optional) desired columns from the
@data slot / data.frame.
Please see also the package "sp" reference manual.
Cheers!
Roland


Jianyun Wu schrieb am 2014-11-28:
> Dear list,

> I usually use 'readOGR()' from rgdal package in R to input the ESRI
> shapefile.
> So the inputted data are SpatialPolygonsDataFrame.

> I am processing the New South Wales, Australia map for a spatial
> analysis.
> There is an island far away from the mainland, which I want to delete
> it
> from the map when I plot NSW.  Because it makes the whole plot small
> due to
> its long distant.

> Below is the area contains the polygons of this island and
> surrounding
> islands. There are 14 "@Polygons" contributing to the entire area.
> From
> some experiments, I know that it is Polygon 3-14 making the distant
> islands.

> Is there a simple way that I can delete those small polygons from
> this area
> polygon and their attributes from the data

> Thank you

> Fred

> str(nsw_lga[153, ])
> Formal class 'SpatialPolygonsDataFrame' [package "sp"] with 5 slots
>   ..@ data       :'data.frame':    1 obs. of  3 variables:
>   .. ..$ STATE_CODE: Factor w/ 9 levels "1","2","3","4",..: 1
>   .. ..$ LGA_CODE11: Factor w/ 565 levels "10050","10110",..: 153
>   .. ..$ LGA_NAME11: Factor w/ 564 levels "Adelaide (C)",..: 483
>   ..@ polygons   :List of 1
>   .. ..$ :Formal class 'Polygons' [package "sp"] with 5 slots
>   .. .. .. ..@ Polygons :List of 14
>   .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
>   .. .. .. .. .. .. ..@ labpt  : num [1:2] 159.1 -31.5
>   .. .. .. .. .. .. ..@ area   : num 3.83e-07
>   .. .. .. .. .. .. ..@ hole   : logi FALSE
>   .. .. .. .. .. .. ..@ ringDir: int 1
>   .. .. .. .. .. .. ..@ coords : num [1:38, 1:2] 159 159 159 159 159
>   ...
>   .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
>   .. .. .. .. .. .. ..@ labpt  : num [1:2] 159.1 -31.5
>   .. .. .. .. .. .. ..@ area   : num 4.69e-07
>   .. .. .. .. .. .. ..@ hole   : logi FALSE
>   .. .. .. .. .. .. ..@ ringDir: int 1
>   .. .. .. .. .. .. ..@ coords : num [1:13, 1:2] 159 159 159 159 159
>   ...
>   .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
>   .. .. .. .. .. .. ..@ labpt  : num [1:2] 159.1 -31.5
>   .. .. .. .. .. .. ..@ area   : num 7.82e-07
>   .. .. .. .. .. .. ..@ hole   : logi FALSE
>   .. .. .. .. .. .. ..@ ringDir: int 1
>   .. .. .. .. .. .. ..@ coords : num [1:31, 1:2] 159 159 159 159 159
>   ...
>   .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
>   .. .. .. .. .. .. ..@ labpt  : num [1:2] 159.1 -31.5
>   .. .. .. .. .. .. ..@ area   : num 1.02e-06
>   .. .. .. .. .. .. ..@ hole   : logi FALSE
>   .. .. .. .. .. .. ..@ ringDir: int 1
>   .. .. .. .. .. .. ..@ coords : num [1:47, 1:2] 159 159 159 159 159
>   ...
>   .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
>   .. .. .. .. .. .. ..@ labpt  : num [1:2] 159.1 -31.5
>   .. .. .. .. .. .. ..@ area   : num 1.14e-06
>   .. .. .. .. .. .. ..@ hole   : logi FALSE
>   .. .. .. .. .. .. ..@ ringDir: int 1
>   .. .. .. .. .. .. ..@ coords : num [1:22, 1:2] 159 159 159 159 159
>   ...
>   .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
>   .. .. .. .. .. .. ..@ labpt  : num [1:2] 159.1 -31.6
>   .. .. .. .. .. .. ..@ area   : num 1.38e-06
>   .. .. .. .. .. .. ..@ hole   : logi FALSE
>   .. .. .. .. .. .. ..@ ringDir: int 1
>   .. .. .. .. .. .. ..@ coords : num [1:24, 1:2] 159 159 159 159 159
>   ...
>   .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
>   .. .. .. .. .. .. ..@ labpt  : num [1:2] 159.1 -31.5
>   .. .. .. .. .. .. ..@ area   : num 1.52e-06
>   .. .. .. .. .. .. ..@ hole   : logi FALSE
>   .. .. .. .. .. .. ..@ ringDir: int 1
>   .. .. .. .. .. .. ..@ coords : num [1:26, 1:2] 159 159 159 159 159
>   ...
>   .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
>   .. .. .. .. .. .. ..@ labpt  : num [1:2] 159.1 -31.5
>   .. .. .. .. .. .. ..@ area   : num 2.05e-06
>   .. .. .. .. .. .. ..@ hole   : logi FALSE
>   .. .. .. .. .. .. ..@ ringDir: int 1
>   .. .. .. .. .. .. ..@ coords : num [1:32, 1:2] 159 159 159 159 159
>   ...
>   .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
>   .. .. .. .. .. .. ..@ labpt  : num [1:2] 159.1 -31.5
>   .. .. .. .. .. .. ..@ area   : num 2.61e-06
>   .. .. .. .. .. .. ..@ hole   : logi FALSE
>   .. .. .. .. .. .. ..@ ringDir: int 1
>   .. .. .. .. .. .. ..@ coords : num [1:36, 1:2] 159 159 159 159 159
>   ...
>   .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
>   .. .. .. .. .. .. ..@ labpt  : num [1:2] 159.1 -31.5
>   .. .. .. .. .. .. ..@ area   : num 4.27e-06
>   .. .. .. .. .. .. ..@ hole   : logi FALSE
>   .. .. .. .. .. .. ..@ ringDir: int 1
>   .. .. .. .. .. .. ..@ coords : num [1:109, 1:2] 159 159 159 159 159
>   ...
>   .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
>   .. .. .. .. .. .. ..@ labpt  : num [1:2] 159.1 -31.5
>   .. .. .. .. .. .. ..@ area   : num 1.42e-05
>   .. .. .. .. .. .. ..@ hole   : logi FALSE
>   .. .. .. .. .. .. ..@ ringDir: int 1
>   .. .. .. .. .. .. ..@ coords : num [1:85, 1:2] 159 159 159 159 159
>   ...
>   .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
>   .. .. .. .. .. .. ..@ labpt  : num [1:2] 159.1 -31.6
>   .. .. .. .. .. .. ..@ area   : num 0.00152
>   .. .. .. .. .. .. ..@ hole   : logi FALSE
>   .. .. .. .. .. .. ..@ ringDir: int 1
>   .. .. .. .. .. .. ..@ coords : num [1:2929, 1:2] 159 159 159 159
>   159 ...
>   .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
>   .. .. .. .. .. .. ..@ labpt  : num [1:2] 142.2 -30.7
>   .. .. .. .. .. .. ..@ area   : num 8.79
>   .. .. .. .. .. .. ..@ hole   : logi FALSE
>   .. .. .. .. .. .. ..@ ringDir: int 1
>   .. .. .. .. .. .. ..@ coords : num [1:5178, 1:2] 144 144 144 144
>   144 ...
>   .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
>   .. .. .. .. .. .. ..@ labpt  : num [1:2] 141.5 -31.9
>   .. .. .. .. .. .. ..@ area   : num 0.0162
>   .. .. .. .. .. .. ..@ hole   : logi TRUE
>   .. .. .. .. .. .. ..@ ringDir: int -1
>   .. .. .. .. .. .. ..@ coords : num [1:131, 1:2] 141 141 141 141 141
>   ...
>   .. .. .. ..@ plotOrder: int [1:14] 13 14 12 11 10 9 8 7 6 5 ...
>   .. .. .. ..@ labpt    : num [1:2] 142.2 -30.7
>   .. .. .. ..@ ID       : chr "152"
>   .. .. .. ..@ area     : num 8.79
>   ..@ plotOrder  : int 1
>   ..@ bbox       : num [1:2, 1:2] 141 -33.4 159.1 -29
>   .. ..- attr(*, "dimnames")=List of 2
>   .. .. ..$ : chr [1:2] "x" "y"
>   .. .. ..$ : chr [1:2] "min" "max"
>   ..@ proj4string:Formal class 'CRS' [package "sp"] with 1 slot
>   .. .. ..@ projargs: chr "+proj=longlat +ellps=GRS80 +no_defs"

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