在R中填充多维数组的值

Question

我想将值填充到R中的多维数组中。我知道如何在循环中实现它们。见下文

a <- array(seq(1, 8), dim = rep(2, 3))

案例1

b <- a
for (i in seq(length = dim(a)[2]))
{
    for (j in seq(length = dim(a)[3]))
    {
        b[,i,j] <- b[,1,1]
    }
}

即 - 填写所有其他列中第一层的第一列：

#, , 1
#
#     [,1] [,2]
#[1,]    1    1
#[2,]    2    2
#
#, , 2
#
#     [,1] [,2]
#[1,]    1    1
#[2,]    2    2

案例2

b <- a
for (i in seq(length = dim(a)[2]))
{
    b[,i,] <- b[,1,]
}

即。填充地层其余列中每个地层的第一列：

#, , 1
#
#     [,1] [,2]
#[1,]    1    1
#[2,]    2    2
#
#, , 2
#
#     [,1] [,2]
#[1,]    5    5
#[2,]    6    6

案例3

b <- a
for (i in seq(length = dim(a)[3]))
{
    b[,,i] <- b[,,1]
}

即。将第一层的内容填入所有其他层：

#, , 1
#
#     [,1] [,2]
#[1,]    1    3
#[2,]    2    4
#
#, , 2
#
#     [,1] [,2]
#[1,]    1    3
#[2,]    2    4

我怎么能把它矢量化？谢谢你的任何建议。

Answer 1

以下是使用索引向量的for循环的概括。

a <- array(seq(1, 24), dim = 2:4)

# a couple of handy index vectors
s2 <- seq(length = dim(a)[2])
s3 <- seq(length = dim(a)[3])

<案例1

B  <-  b <- a
for (i in seq(length = dim(a)[2]))
{
    for (j in seq(length = dim(a)[3]))
    {
        b[,i,j] <- b[,1,1]
    }
}


B[,s2,s3] <- B[,1,1]
identical(B,b)

<案例2

B  <-  b <- a
for (i in seq(length = dim(a)[2]))
{
    b[,i,] <- b[,1,]
}

# this is the tricky one.  The assignment works
# because we perumte the the matrix B so that we're 
# assigning to the last index.
B<- aperm(B,c(1,3,2)) 
B[,,s2] <- B[,,1]
B<- aperm(B,c(1,3,2)) 
identical(B,b)

<案例3

B  <-  b <- a
for (i in seq(length = dim(a)[3]))
{
    b[,,i] <- b[,,1]
}

B[,,s3] <- B[,,1]
identical(B,b)