CODEWITHSUNDEEP
rsubsetspatial
bee guy
bee guy

Reputation: 439

Troubleshooting why subsetting of spatial object does not work

I am trying to subset a 'SpatialPolygonsDataFrame' in R, but the methods proposed in other threads seem not to work. I am using R version 3.3.2 and I am accessing it through R studio on a mac.

Unfortunately, I cannot provide my dataset, (because I cannot subset my data).

This,

sp2 <- sp1[sp1@data$compound_found == 1, ]

produced the following error:

Error in sp1[sp1@data$compound_found == 1, ] :    cannot get a slot ("Polygons") from an object of type "NULL"

despite 

sp1@data$compound_found == 1

[1] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
FALSE FALSE 
[14] FALSE  TRUE FALSE FALSE  TRUE  TRUE FALSE FALSE FALSE
FALSE FALSE  TRUE  TRUE 
[27]  TRUE  TRUE FALSE  TRUE  TRUE FALSE  TRUE
TRUE FALSE FALSE FALSE  TRUE

sp2 <- sp1["compound_found" == 1, ]

does not create an error, but creates an empty object 

nrow(sp2@data) # returns 0

Any explanation why I cannot subset the way I was trying? How could I do it instead?

EDIT:

class(sp1)

returns

[1] "SpatialPolygonsDataFrame"
attr(,"package")
[1] "sp"

Upvotes: 0

Views: 2600

Answers (1)

Djork
Djork

Reputation: 3369

Edited to describe troubleshooting that arrived at solution with help from OP.

A SpatialPolygonsDataFrame usually can be subsetted as the OP has done above in the original question: 

sp1[sp1@data$compound_found == 1, ]

Not sure where the error comes from without seeing the data. To troubleshoot, you can examine the structure of SpatialPolygonsDataFrame to see where the error might be coming from.

str(sp1)

You can also separately subset @data and @polygons to check if it's pulling the right elements.

If you want to subset sp1@data you can use:

sp1@data[1:ncol(sp1@data)][sp1@data$compound_found == 1,]

To get sp1@polygons:

sp1@polygons[sp1@data$compound_found == 1]

Note that @data and @polygons should be the same length. See http://www.dpi.inpe.br/gilberto/tutorials/software/R-contrib/sp/html/SpatialPolygons.html

"data: the number of rows in data should equal the number of Polygons-class objects in Sr"

Check that nrow(sp1@data) and length(sp1@polygons) are the same.

Upvotes: 1

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