優雅地評估R中兩個值向量的兩個變量的函數？

Question

我有兩個變量的函數和每個變量的時間間隔。最後我想提出一個熱點圖，其中Point（x，y）表示該點處函數的值，所以我想在相應的時間間隔內爲兩個值的每個組合計算函數。 該函數有兩個double值。 我找到了outer（）函數，但我不完全確定它正在做我想要的。有沒有快速解決這個問題？

謝謝！

Answer 1

outer確實是一個好主意，假設（x，y）點形成一個矩形網格。例如，它至少比mapply更快。

f <- function(x,y){sprintf("heat(%3.1f,%3.1f)",x,y)} 

X <- 0.5*(0:12) 
Y <- 0.3*(0:3) 

X.matrix <- matrix(X,length(X),length(Y)) 
Y.matrix <- matrix(Y,length(X),length(Y),byrow=TRUE) 

system.time(for (i in 1:100000){ heat.1 <- outer(X,Y,"f") }) 
system.time(for (i in 1:100000){ heat.2 <- matrix(mapply("f",X.matrix,Y.matrix),length(X))}) 

。

> system.time(for (i in 1:100000){ heat.1 <- outer(X,Y,"f") }) 
    user system elapsed 
    22.71 0.00 22.83 

> system.time(for (i in 1:100000){ heat.2 <- matrix(mapply("f",X.matrix,Y.matrix),length(X))}) 
    user system elapsed 
    57.03 0.02 57.53 

。

> identical(heat.1,heat.2) 
[1] TRUE 
> heat.1 
     [,1]   [,2]   [,3]   [,4]   
[1,] "heat(0.0,0.0)" "heat(0.0,0.3)" "heat(0.0,0.6)" "heat(0.0,0.9)" 
[2,] "heat(0.5,0.0)" "heat(0.5,0.3)" "heat(0.5,0.6)" "heat(0.5,0.9)" 
[3,] "heat(1.0,0.0)" "heat(1.0,0.3)" "heat(1.0,0.6)" "heat(1.0,0.9)" 
[4,] "heat(1.5,0.0)" "heat(1.5,0.3)" "heat(1.5,0.6)" "heat(1.5,0.9)" 
[5,] "heat(2.0,0.0)" "heat(2.0,0.3)" "heat(2.0,0.6)" "heat(2.0,0.9)" 
[6,] "heat(2.5,0.0)" "heat(2.5,0.3)" "heat(2.5,0.6)" "heat(2.5,0.9)" 
[7,] "heat(3.0,0.0)" "heat(3.0,0.3)" "heat(3.0,0.6)" "heat(3.0,0.9)" 
[8,] "heat(3.5,0.0)" "heat(3.5,0.3)" "heat(3.5,0.6)" "heat(3.5,0.9)" 
[9,] "heat(4.0,0.0)" "heat(4.0,0.3)" "heat(4.0,0.6)" "heat(4.0,0.9)" 
[10,] "heat(4.5,0.0)" "heat(4.5,0.3)" "heat(4.5,0.6)" "heat(4.5,0.9)" 
[11,] "heat(5.0,0.0)" "heat(5.0,0.3)" "heat(5.0,0.6)" "heat(5.0,0.9)" 
[12,] "heat(5.5,0.0)" "heat(5.5,0.3)" "heat(5.5,0.6)" "heat(5.5,0.9)" 
[13,] "heat(6.0,0.0)" "heat(6.0,0.3)" "heat(6.0,0.6)" "heat(6.0,0.9)" 
>