R語言grid包just參數如何just圖形位置

思路

  grid的畫圖函數都含有just，但是just參數的是怎么調節圖形位置的總是讓人非常費解，於是便寫了代碼來一探究竟。
  思路非常簡單：放一個2*2的布局viewport，每個布局里面放一個viewport，每個viewport都用了不同的just參數。just之后的矩形用藍色顯示，中心點的移動用箭頭表示出來， 這樣每個參數對應圖形怎么移動的都能一目了然。從以下的代碼也能學到如何安排布局， 如何使用grobX和grobY獲得grob對象的坐標， 如何進行基本的viewport切換等。

代碼

library(grid)

grid.newpage()  # new page
pushViewport(viewport(layout = grid.layout(2,2))) # 2 *2 layout

# just top
pushViewport(viewport(layout.pos.col = 1, layout.pos.row = 1))
grid.rect()
r1 <- rectGrob(0.5, 0.5, width = 0.2, height = 0.2, name = "r1")
r2 <- rectGrob(0.5, 0.5, width = 0.2, height = 0.2, just = c("top"),gp=gpar(col="blue"), name = "r2")
grid.draw(r1)
grid.draw(r2)
grid.segments(0.5,0.5,grobX(r2, 90), grobY(r2, 0), arrow=arrow(angle=15, type="closed"), gp=gpar(fill="black"))
grid.text("just: top" ,0.6, 0.8)
upViewport()

# just left and top
pushViewport(viewport(layout.pos.col = 1, layout.pos.row = 2))
grid.rect()
r1 <- rectGrob(0.5, 0.5, width = 0.2, height = 0.2, name="r1")
r2 <- rectGrob(0.5, 0.5, width = 0.2, height = 0.2, just = c("left", "top"), gp=gpar(col="blue"), name="r2")
grid.draw(r1)
grid.draw(r2)
grid.segments(0.5, 0.5, grobX(r2, 90), grobY(r2, 0), arrow=arrow(angle=15, type="closed",), gp=gpar(fill="black"))
grid.text("just: left and top", 0.6, 0.8)
upViewport()

# just left and bottom
pushViewport(viewport(layout.pos.col = 2, layout.pos.row = 1))
grid.rect()
r1 <- rectGrob(0.5, 0.5, width = 0.2, height = 0.2, name="r1")
r2 <- rectGrob(0.5, 0.5, width = 0.2, height = 0.2, just = c("left", "bottom"), gp=gpar(col="blue"), name="r2")
grid.draw(r1)
grid.draw(r2)
grid.segments(0.5, 0.5,grobX(r2, 90), grobY(r2, 0), arrow=arrow(angle=15, type="closed",), gp=gpar(fill="black"))
grid.text("just: left and bottom", 0.6, 0.8)
upViewport()

# just right bottom
pushViewport(viewport(layout.pos.col = 2, layout.pos.row = 2))
grid.rect()
r1 <- rectGrob(0.5, 0.5, width = 0.2, height = 0.2, name="r1")
r2 <- rectGrob(0.5, 0.5, width = 0.2, height = 0.2, just = c("right", "bottom"), gp=gpar(col="blue"), name = "r2")
grid.draw(r1)
grid.draw(r2)
grid.segments(0.5,0.5,grobX(r2, 90), grobY(r2, 0), arrow=arrow(angle=15, type="closed",), gp=gpar(fill="black"))
grid.text("just: right and bottom", 0.6, 0.8)
upViewport()

結果

結論

• just參數對圖形進行相反的調節，比如想向上調節圖形，就得調節just="bottom"，也可以理解為真實位置相對於畫圖位置，比如真實位置要比畫圖位置要低，就用just="bottom“
• grobX角度為90時， grobY 角度為0時，可獲得圖形的中心位置， grobX 為0時X位置在圖形的最右， grobY 為0時Y位置在圖形的中間