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是否可以以某种方式轻松处理Spatial*DataFrame（* = 点、线、多边形、像素、网格...）中的数据？特别是我很难为它分配值并使用它们进行操作：

require(gstat)
data(meuse)
coordinates(meuse) = ~x+y
data(meuse.grid)
gridded(meuse.grid) = ~x+y

######## 1) assigning value

meuse[1,'zinc'] <- NA
# Error in meuse[1, "zinc"] <- NA : object of type 'S4' is not subsettable
as.data.frame(meuse)[1,'zinc'] <- NA
# Error in as.data.frame(meuse)[1, "zinc"] <- NA : 
#   could not find function "as.data.frame<-"

######## 2) operating with values

meuse[, 'zinc'] + 2
# Error in meuse[, "zinc"] + 2 : non-numeric argument to binary operator

对于这两种情况，我都发现了非常丑陋的解决方法：

# ad 1)
meuse2 <- as.data.frame(meuse)
meuse2[1, 'zinc'] <- NA
meuse2 <- SpatialPointsDataFrame(SpatialPoints(meuse), meuse2)

# ad 2)
as.data.frame(meuse)[, 'zinc'] + 2

但这些只是初学者的尝试，太丑陋和复杂......在R中一定要容易得多！

4

2 回答 2

6

You can do this like this: 

meuse$zinc[1] <- NA

or, better since you can use a variable name rather than literal:

aname <- 'zinc'
meuse[[aname]][1] <- NA

It seems that other pathways to this are not provided as methods, but they could be added. I'm not sure why this is the case, but originally the *DataFrame part was built as an AttributeList in sp since R's actual data.frame was inefficient with rownames at the time, but that is ancient history and all fixed now.

You could expect that these would work, like a normal data.frame but they do not:

meuse[1,'zinc'] <- NA
meuse[1,][['zinc']] <- NA
meuse[1,]$zinc <- NA

It's probably best to avoid the @ operator if you can, because it is for developers to hide inside the code they provide to users, i.e. it's subverting their API if you don't use the methods provided. There's no massive danger in it, except that the developers might change the API and your code won't work, and you might corrupt the object by modifying one part but not another in the way the object was designed, so you shouldn't use it except privately or in code you maintain actively (I think it's safe in this instance but avoid it generally if you can). See ?"@" and ?"slot" for the basics.

于 2013-08-01T04:54:03.067 回答
5

对于 Spatial*DataFrame 对象，您可以使用“@data”访问 data.frame 插槽，并且通常的 data.frame 操作应该可以工作。使用您的示例，

 meuse@data[1, 'zinc'] <- NA

给

 str(meuse@data)
'data.frame':   155 obs. of  12 variables:
 $ cadmium: num  11.7 8.6 6.5 2.6 2.8 3 3.2 2.8 2.4 1.6 ...
 $ copper : num  85 81 68 81 48 61 31 29 37 24 ...
 $ lead   : num  299 277 199 116 117 137 132 150 133 80 ...
 $ zinc   : num  NA 1141 640 257 269 ...
 ...
于 2013-07-31T19:46:37.527 回答