计算两点之间的所有可能坡度

如果你需要 choose(n, 2) 斜坡间 n 数 (x, y) 点、用途

xy <- cbind(x, y)
library(RcppAlgos)
ind <- comboGeneral(nrow(xy), 2)
d <- xy[ind[, 2], ] - xy[ind[, 1], ]
slope <- d[, 2] / d[, 1]

我不在用 combn 来自R核心的功能。见 Product between all combinations of a vector's elements 用于案例研究。

使用末尾注释中的数据,假设需要选择2个坡度。

slopes <- c(combn(y, 2, diff) / combn(x, 2, diff))
slopes
## [1] -3.7970202 -1.4062612 -3.8066222 -3.1325626 -0.9648338 -3.8171698
## [7] -2.5220191 -0.3885287 -0.5732387  4.1033272

这些分别是这些对的斜率:

nms <- combn(n, 2, paste, collapse = ":")
nms
## [1] "1:2" "1:3" "1:4" "1:5" "2:3" "2:4" "2:5" "3:4" "3:5" "4:5"

all.equal(slopes, slopes2[order(nms2)])

补充

如果速度不够快,试试看 combnPrim 从GRBASE(在生物导体中)代替:

library(gRBase)

xx <- combnPrim(x, 2)
yy <- combnPrim(y, 2)
slopes2 <- (yy[2, ] - yy[1, ]) / (xx[2, ] - xx[1, ])
slopes2
## [1] -3.7970202 -1.4062612 -0.9648338 -3.8066222 -3.8171698 -0.3885287
## [7] -3.1325626 -2.5220191 -0.5732387  4.1033272

nms2 <- apply(combnPrim(n, 2), 2, paste, collapse = ":")
## [1] "1:2" "1:3" "2:3" "1:4" "2:4" "3:4" "1:5" "2:5" "3:5" "4:5"

all.equal(slopes, slopes2[order(nms2)])
## [1] TRUE

注释

我们使用以下输入:

set.seed(123)
n <- 5
x <- rnorm(n)
y <- rnorm(n)