R语言中“@”运算符的含义？

Question

我遇到了以下情况，但我还没有弄清楚“@”运算符的用途。那里有什么意义？我没有heads/tails的R手册语言。

library(lattice)
library(sp)

data(meuse)
coordinates(meuse) <- ~x+y
proj4string(meuse) <- CRS("+init=epsg:28992")

p <- xyplot(copper ~ cadmium, data = meuse@data, col = "grey", pch = 20, cex = 2)

R 手册说

Usage object@name object@name <- value

Extract or replace the contents of a slot in a object with a formal (S4) class structure. These operators support the formal classes of package methods, and are enabled only when package methods is loaded (as per default). See slot for further details, in particular for the differences between slot() and the @ operator.

It is checked that object is an S4 object (see isS4), and it is an error to attempt to use @ on any other object. (There is an exception for name .Data for internal use only.) The replacement operator checks that the slot already exists on the object (which it should if the object is really from the class it claims to be).

我检查了 "meuse" 的结构，没有发现对名为 "data".

的槽的引用

Answer 1

meuse 是 S4 对象

isS4(meuse)
[1] TRUE

如果采用 meuse (str_meuse) 的结构，您会看到一些字段用 @ 运算符表示，包括一个名为 data 的字段。可以使用 @ 访问这些槽，类似于使用 $ 运算符访问其他对象中的其他槽的方式。所以 meuse@data 给你 meuse 对象的 data 部分。

str(meuse)

Formal class 'SpatialPointsDataFrame' [package "sp"] with 5 slots
  ..@ data       :'data.frame': 155 obs. of  12 variables:
  .. ..$ cadmium: num [1:155] 11.7 8.6 6.5 2.6 2.8 3 3.2 2.8 2.4 1.6 ...
  .. ..$ copper : num [1:155] 85 81 68 81 48 61 31 29 37 24 ...
  .. ..$ lead   : num [1:155] 299 277 199 116 117 137 132 150 133 80 ...
  .. ..$ zinc   : num [1:155] 1022 1141 640 257 269 ...
  .. ..$ elev   : num [1:155] 7.91 6.98 7.8 7.66 7.48 ...
  .. ..$ dist   : num [1:155] 0.00136 0.01222 0.10303 0.19009 0.27709 ...
  .. ..$ om     : num [1:155] 13.6 14 13 8 8.7 7.8 9.2 9.5 10.6 6.3 ...
  .. ..$ ffreq  : Factor w/ 3 levels "1","2","3": 1 1 1 1 1 1 1 1 1 1 ...
  .. ..$ soil   : Factor w/ 3 levels "1","2","3": 1 1 1 2 2 2 2 1 1 2 ...
  .. ..$ lime   : Factor w/ 2 levels "0","1": 2 2 2 1 1 1 1 1 1 1 ...
  .. ..$ landuse: Factor w/ 15 levels "Aa","Ab","Ag",..: 4 4 4 11 4 11 4 2 2 15 ...
  .. ..$ dist.m : num [1:155] 50 30 150 270 380 470 240 120 240 420 ...
  ..@ coords.nrs : int [1:2] 1 2
  ..@ coords     : num [1:155, 1:2] 181072 181025 181165 181298 18130

看看子集是如何工作的？

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  1022 1141 640 257 269 ...
 $ elev   : num  7.91 6.98 7.8 7.66 7.48 ...
 $ dist   : num  0.00136 0.01222 0.10303 0.19009 0.27709 ...
 $ om     : num  13.6 14 13 8 8.7 7.8 9.2 9.5 10.6 6.3 ...
 $ ffreq  : Factor w/ 3 levels "1","2","3": 1 1 1 1 1 1 1 1 1 1 ...
 $ soil   : Factor w/ 3 levels "1","2","3": 1 1 1 2 2 2 2 1 1 2 ...
 $ lime   : Factor w/ 2 levels "0","1": 2 2 2 1 1 1 1 1 1 1 ...
 $ landuse: Factor w/ 15 levels "Aa","Ab","Ag",..: 4 4 4 11 4 11 4 2 2 15 ...
 $ dist.m : num  50 30 150 270 380 470 240 120 240 420 ...

R语言中“@”运算符的含义？

Meaning of "@" operator in R language?

r

ggplot2

lattice