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，可是just參數的是怎麼調節圖形位置的老是讓人很是費解，因而便寫了代碼來一探究竟。
  思路很是簡單：放一個2*2的佈局viewport，每一個佈局裏面放一個viewport，每一個viewport都用了不一樣的just參數。just以後的矩形用藍色顯示，中心點的移動用箭頭表示出來， 這樣每一個參數對應圖形怎麼移動的都能一目瞭然。從如下的代碼也能學到如何安排佈局， 如何使用grobX和grobY得到grob對象的座標， 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，好比想向上調節圖形，就得調節just="bottom"，也能夠理解爲真實位置相對於畫圖位置，好比真實位置要比畫圖位置要低，就用just="bottom「
• grobX角度爲90時， grobY 角度爲0時，可得到圖形的中心位置， grobX 爲0時X位置在圖形的最右， grobY 爲0時Y位置在圖形的中間