- [R如何計算levelplot

Question

欲levelplot的水平內計算所述區域之內的區域...

例如：

在火山數據的130座140山之間的區域：

contour(volcano) 
win.graph() 
dd<-levelplot(volcano, at=c(130,140)) 

我想只計算由DD繪製的粉紅色區域，

有什麼建議？ :-)

注：DD的結構是：

str(dd) 

    List of 45 
$ formula   :Class 'formula' length 3 z ~ row * column 
    .. ..- attr(*, ".Environment")=<environment: 0x031e53ec> 
$ as.table   : logi FALSE 
$ aspect.fill  : logi FALSE 
$ legend   :List of 1 
    ..$ right:List of 2 
    .. ..$ fun : chr "draw.colorkey" 
    .. ..$ args:List of 2 
    .. .. ..$ key :List of 2 
    .. .. .. ..$ at : num [1:2] 130 140 
    .. .. .. ..$ space: chr "right" 
    .. .. ..$ draw: logi FALSE 
$ panel   : chr "panel.levelplot" 
$ page    : NULL 
$ layout   : NULL 
$ skip    : logi FALSE 
$ strip   : logi FALSE 
$ strip.left  : logi FALSE 
$ xscale.components:function (lim, packet.number = 0, packet.list = NULL, top = TRUE, ...) 
$ yscale.components:function (lim, packet.number = 0, packet.list = NULL, right = TRUE, ...) 
$ axis    :function (side = c("top", "bottom", "left", "right"), scales, components, as.table, labels = c("default", 
    "yes", "no"), ticks = c("default", "yes", "no"), ..., prefix = lattice.getStatus("current.prefix")) 
$ xlab    : chr "row" 
$ ylab    : chr "column" 
$ xlab.default  : chr "row" 
$ ylab.default  : chr "column" 
$ xlab.top   : NULL 
$ ylab.right  : NULL 
$ main    : NULL 
$ sub    : NULL 
$ x.between  : num 0 
$ y.between  : num 0 
$ par.settings  : NULL 
$ plot.args  : NULL 
$ lattice.options : NULL 
$ par.strip.text : NULL 
$ index.cond  :List of 1 
    ..$ : int 1 
$ perm.cond  : int 1 
$ condlevels  :List of 1 
    ..$ : chr "1" 
$ call    : language levelplot(volcano, at = c(130, 140)) 
$ x.scales   :List of 26 
    ..$ draw   : logi TRUE 
    ..$ axs   : chr "r" 
    ..$ tck   : num [1:2] 1 1 
    ..$ tick.number : num 5 
    ..$ at   : logi FALSE 
    ..$ labels  : logi FALSE 
    ..$ log   : logi FALSE 
    ..$ alternating : num [1:2] 1 2 
    ..$ relation  : chr "same" 
    ..$ abbreviate : logi FALSE 
    ..$ minlength  : num 4 
    ..$ limits  : NULL 
    ..$ format  : NULL 
    ..$ equispaced.log: logi TRUE 
    ..$ lty   : logi FALSE 
    ..$ lwd   : logi FALSE 
    ..$ cex   : logi [1:2] FALSE FALSE 
    ..$ rot   : logi [1:2] FALSE FALSE 
    ..$ col   : logi FALSE 
    ..$ col.line  : logi FALSE 
    ..$ alpha   : logi FALSE 
    ..$ alpha.line : logi FALSE 
    ..$ font   : logi FALSE 
    ..$ fontfamily : logi FALSE 
    ..$ fontface  : logi FALSE 
    ..$ lineheight : logi FALSE 
$ y.scales   :List of 26 
    ..$ draw   : logi TRUE 
    ..$ axs   : chr "r" 
    ..$ tck   : num [1:2] 1 1 
    ..$ tick.number : num 5 
    ..$ at   : logi FALSE 
    ..$ labels  : logi FALSE 
    ..$ log   : logi FALSE 
    ..$ alternating : num [1:2] 1 2 
    ..$ relation  : chr "same" 
    ..$ abbreviate : logi FALSE 
    ..$ minlength  : num 4 
    ..$ limits  : NULL 
    ..$ format  : NULL 
    ..$ equispaced.log: logi TRUE 
    ..$ lty   : logi FALSE 
    ..$ lwd   : logi FALSE 
    ..$ cex   : logi [1:2] FALSE FALSE 
    ..$ rot   : logi [1:2] FALSE FALSE 
    ..$ col   : logi FALSE 
    ..$ col.line  : logi FALSE 
    ..$ alpha   : logi FALSE 
    ..$ alpha.line : logi FALSE 
    ..$ font   : logi FALSE 
    ..$ fontfamily : logi FALSE 
    ..$ fontface  : logi FALSE 
    ..$ lineheight : logi FALSE 
$ panel.args.common:List of 5 
    ..$ x  : int [1:5307] 1 2 3 4 5 6 7 8 9 10 ... 
    ..$ y  : int [1:5307] 1 1 1 1 1 1 1 1 1 1 ... 
    ..$ z  : num [1:5307] 100 101 102 103 104 105 105 106 107 108 ... 
    ..$ at : num [1:2] 130 140 
    ..$ region: logi TRUE 
$ panel.args  :List of 1 
    ..$ :List of 1 
    .. ..$ subscripts: int [1:5307] 1 2 3 4 5 6 7 8 9 10 ... 
$ packet.sizes  : num 5307 
$ x.limits   : num [1:2] 0.5 87.5 
$ y.limits   : num [1:2] 0.5 61.5 
$ x.used.at  : NULL 
$ y.used.at  : NULL 
$ x.num.limit  : NULL 
$ y.num.limit  : NULL 
$ aspect.ratio  : num 0.701 
$ prepanel.default : chr "prepanel.default.levelplot" 
$ prepanel   : NULL 
- attr(*, "class")= chr "trellis" 

Answer 1

關注的levelplot輸出可能比你實際需要的更復雜。以下代碼直接計算130和140之間的所有單元格的總面積：

# compute area represented by each cell in the matrix. 
# `?volcano` says this is a regular 10m x 10m grid: 
column_widths <- rep(10, ncol(volcano)) 
row_heights <- rep(10, nrow(volcano)) 
cell_areas <- row_heights %*% t(column_widths) 

# which cells are >130, <140: 
pink_cells <- (volcano > 130) & (volcano < 140) 

# sum up area of pink_cells 
(area <- sum(cell_areas[pink_cells])) 

## [1] 43800