在R中用曲线(s-ish曲线)连接两个点

Question

假设我想生成一种类似下面的树结构:

plot(0, type="n",xlim=c(0, 5), ylim=c(-3, 8), axes=FALSE, xlab="", ylab="", main="")
points(1, 2.5)
points(3, 5)
points(3, 0)
lines(c(1, 3), c(2.5, 5))
lines(c(1, 3), c(2.5, 0))
text(1, 2.5, adj=1, label="Parent   ")
text(3, 5, adj=0, label="   Child 1")
text(3, 0, adj=0, label="   Child 2")

我想知道是否有一种方法R可以产生类似于下面不同程度的S曲线的曲线.至关重要的是,如果能够在不诉诸的情况下创造这样的线路,那就太棒了ggplot.

编辑删除并作出答案

Answer 1

按照@ thelatemail的建议,我决定让我的编辑得到一个答案.我的解决方案基于@thelatemail的答案.

我写了一个小函数来绘制曲线,它使用了逻辑函数:

#Create the function
curveMaker <- function(x1, y1, x2, y2, ...){
    curve( plogis( x, scale = 0.08, loc = (x1 + x2) /2 ) * (y2-y1) + y1, 
                   x1, x2, add = TRUE, ...)
}

下面是一个工作示例.在这个例子中,我想为3个级别的分类法创建一个图:parent- > 2 children- > 20 grandchildren.一个孩子有12个孙子,另一个孩子有8个孩子.

#Prepare data:
parent <- c(1, 16)
children <- cbind(2, c(8, 28))
grandchildren <- cbind(3, (1:20)*2-1)
labels <- c("Parent ", paste("Child ", 1:2), paste(" Grandchild", 1:20) )


#Make a blank plot canvas
plot(0, type="n", ann = FALSE, xlim = c( 0.5, 3.5 ), ylim = c( 0.5, 39.5 ), axes = FALSE )

#Plot curves
#Parent and children
invisible( mapply( curveMaker, 
                   x1 = parent[ 1 ], 
                   y1 = parent[ 2 ], 
                   x2 = children[ , 1 ], 
                   y2 = children[ , 2 ], 
                   col = gray( 0.6, alpha = 0.6 ), lwd = 1.5 ) )

#Children and grandchildren
invisible( mapply( curveMaker, 
                   x1 = children[ 1, 1 ], 
                   y1 = children[ 1, 2 ], 
                   x2 = grandchildren[ 1:8 , 1 ], 
                   y2 = grandchildren[ 1:8, 2 ], 
                   col = gray( 0.6, alpha = 0.6 ), lwd = 1.5 ) ) 
invisible( mapply( curveMaker, 
                   x1 = children[ 2, 1 ], 
                   y1 = children[ 2, 2 ], 
                   x2 = grandchildren[ 9:20 , 1 ], 
                   y2 = grandchildren[ 9:20, 2 ], 
                   col = gray( 0.6, alpha = 0.6 ), lwd = 1.5 ) )
#Plot text
text( x = c(parent[1], children[,1], grandchildren[,1]), 
      y = c(parent[2], children[,2], grandchildren[,2]),
      labels = labels,
      pos = rep(c(2, 4), c(3, 20) ) ) 

#Plot points
points( x = c(parent[1], children[,1], grandchildren[,1]),
        y = c(parent[2], children[,2], grandchildren[,2]), 
        pch = 21, bg = "white", col="#3182bd", lwd=2.5, cex=1)