如何在R中以特定方式乘以两个向量？

Question

我在R中有两个向量：

 a = seq(100, 10000, by=100)
 b = c(0.05, 0.01, 0.005, 0.001)

如何创建一个看起来像

的4 x 100矩阵

 a1*b1 a1*b2 ... a1*bn
 a2*b1 a2*b2 ... a2*bn

等？ a和b的大小/组件可能会发生变化，因此我需要一种通用的方法来执行此操作。

Answer 1

我猜你正在寻找

outer(a, b, "*")
#     [,1] [,2] [,3] [,4]
#[1,]    5    1  0.5  0.1
#[2,]   10    2  1.0  0.2
#[3,]   15    3  1.5  0.3
#[4,]   20    4  2.0  0.4
#[5,]   25    5  2.5  0.5
#[6,]   30    6  3.0  0.6
#[7,]   35    7  3.5  0.7
#[8,]   40    8  4.0  0.8
#[9,]   45    9  4.5  0.9
#[10,]   50   10  5.0  1.0
#...

或其转置

t(outer(a, b, "*"))
#     [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12] [,13] [,14]
#[1,]  5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0    50  55.0  60.0  65.0  70.0
#[2,]  1.0  2.0  3.0  4.0  5.0  6.0  7.0  8.0  9.0    10  11.0  12.0  13.0  14.0
#[3,]  0.5  1.0  1.5  2.0  2.5  3.0  3.5  4.0  4.5     5   5.5   6.0   6.5   7.0
#[4,]  0.1  0.2  0.3  0.4  0.5  0.6  0.7  0.8  0.9     1   1.1   1.2   1.3   1.4
#     [,15] [,16] [,17] [,18] [,19] [,20] [,21] [,22] [,23] [,24] [,25] [,26]
#[1,]  75.0  80.0  85.0  90.0  95.0   100 105.0 110.0 115.0 120.0 125.0 130.0
#[2,]  15.0  16.0  17.0  18.0  19.0    20  21.0  22.0  23.0  24.0  25.0  26.0
#[3,]   7.5   8.0   8.5   9.0   9.5    10  10.5  11.0  11.5  12.0  12.5  13.0
#[4,]   1.5   1.6   1.7   1.8   1.9     2   2.1   2.2   2.3   2.4   2.5   2.6
#...