[英]Nested for loop for evaluating surrounding cells of matrix in R
I have a 7x7 matrix: 我有一个7x7矩阵:
Mat<-matrix(nrow=7,ncol=7)
With certain elements: 有某些要素:
Mat[2,2]<-37
Mat[2,4]<-39
Mat[2,6]<-24
Mat[4,2]<-35
Mat[4,4]<-36
Mat[4,6]<-26
Mat[6,2]<-26
Mat[6,4]<-31
Mat[6,6]<-39
I am generating random elements and want to test if they add up to the specified values 我正在生成随机元素,并想测试它们是否加起来指定的值
I have written the following code: 我写了以下代码:
TF<-c()
TF[1]<-isTRUE(Mat[2,2]==sum(Mat[1,1],Mat[1,2],Mat[1,3],Mat[2,1],Mat[2,3],Mat[3,1],Mat[3,2],Mat[3,3]))
TF[2]<-isTRUE(Mat[2,4]==sum(Mat[1,3],Mat[1,4],Mat[1,5],Mat[2,3],Mat[2,5],Mat[3,3],Mat[3,4],Mat[3,5]))
TF[3]<-isTRUE(Mat[2,6]==sum(Mat[1,5],Mat[1,6],Mat[1,7],Mat[2,5],Mat[2,7],Mat[3,5],Mat[3,6],Mat[3,7]))
TF[4]<-isTRUE(Mat[4,2]==sum(Mat[3,1],Mat[3,2],Mat[3,3],Mat[4,3],Mat[4,5],Mat[5,1],Mat[5,2],Mat[5,3]))
TF[5]<-isTRUE(Mat[4,4]==sum(Mat[3,3],Mat[3,4],Mat[3,5],Mat[4,3],Mat[4,5],Mat[5,3],Mat[5,4],Mat[5,5]))
TF[6]<-isTRUE(Mat[4,6]==sum(Mat[3,5],Mat[3,6],Mat[3,7],Mat[4,5],Mat[4,7],Mat[5,5],Mat[5,6],Mat[5,7]))
TF[7]<-isTRUE(Mat[6,2]==sum(Mat[5,1],Mat[5,2],Mat[5,3],Mat[6,1],Mat[6,3],Mat[7,1],Mat[7,2],Mat[7,3]))
TF[8]<-isTRUE(Mat[6,4]==sum(Mat[5,3],Mat[5,4],Mat[5,5],Mat[6,3],Mat[6,5],Mat[7,3],Mat[7,4],Mat[7,5]))
TF[9]<-isTRUE(Mat[6,6]==sum(Mat[5,5],Mat[5,6],Mat[5,7],Mat[6,5],Mat[6,7],Mat[7,5],Mat[7,6],Mat[7,7]))
Now i am trying to make it more efficient with a nested for loop: 现在我试图通过嵌套for循环使其更有效:
O<-c(2,4,6)
for (G in O)
{
for (H in O)
{
TF[]<-isTRUE(Mat[G,H]==sum(Mat[G-1,H-1],Mat[G-1,H],Mat[G-1,H+1],Mat[G,H-1],Mat[G,H+1],Mat[G+1,H-1],Mat[G+1,H],Mat[G+1,H+1]))
}
}
The problem is that the vector element will be overwritten and it does not make any sense to add another for loop. 问题是向量元素将被覆盖,并且添加另一个for循环没有任何意义。 I also have problem to find a way to rerun the simulation if one false is found.
如果发现一个错误,我也有问题找到重新运行模拟的方法。
Let's start first by answering the following question: 让我们首先回答以下问题:
How do you compute the sum of every surrounding cell for each cell in a matrix? 如何计算矩阵中每个单元格的每个周围单元格的总和?
This is actually not trivial as far as I can tell (curious to see if anyone else comes up with something cool). 据我所知,这实际上并非微不足道(好奇地看看是否有其他人想出了一些很酷的东西)。 Here is a potential solution, though not even close to being succinct.
这是一个潜在的解决方案,尽管不是很简洁。 Let's start by seeing the results of the function.
让我们从看到函数的结果开始。 Here we will create matrices of only 1 so we can check that the results make sense (corners should add to 3 since there are only three contiguous cells, insides to 8, etc.):
这里我们将创建只有1的矩阵,因此我们可以检查结果是否有意义(角应该加到3,因为只有三个连续的单元格,内部为8,等等):
> compute_neighb_sum(matrix(1, nrow=3, ncol=3))
[,1] [,2] [,3]
[1,] 3 5 3
[2,] 5 8 5
[3,] 3 5 3
> compute_neighb_sum(matrix(1, nrow=3, ncol=5))
[,1] [,2] [,3] [,4] [,5]
[1,] 3 5 5 5 3
[2,] 5 8 8 8 5
[3,] 3 5 5 5 3
> compute_neighb_sum(matrix(1, nrow=7, ncol=7))
[,1] [,2] [,3] [,4] [,5] [,6] [,7]
[1,] 3 5 5 5 5 5 3
[2,] 5 8 8 8 8 8 5
[3,] 5 8 8 8 8 8 5
[4,] 5 8 8 8 8 8 5
[5,] 5 8 8 8 8 8 5
[6,] 5 8 8 8 8 8 5
[7,] 3 5 5 5 5 5 3
This works! 这有效!
Now, let's answer your actual question : 现在,让我们回答您的实际问题 :
compute_neighb_sum(mx) == mx
and this should return TRUE
for all cells that are equal to the sum of their surroundings. 对于所有等于周围环境总和的单元格,这应该返回
TRUE
。 Lets confirm: 让我们确认:
mx <- matrix(1, nrow=7, ncol=7)
mx[cbind(c(3, 6), c(3, 6))] <- 8 # make two interior cells equal two 8, which will be equal to sum of surroundings
which(compute_neighb_sum(mx) == mx, arr.ind=T) # you should look at `mx` to see what's going on
Sure enough, we get back the coordinates that we expect: 果然,我们回到了我们期望的坐标:
row col
[1,] 3 3
[2,] 6 6
Now, here is the function: 现在,这是功能:
compute_neighb_sum <- function(mx) {
mx.ind <- cbind( # create a 2 wide matrix of all possible indices in input
rep(seq.int(nrow(mx)), ncol(mx)),
rep(seq.int(ncol(mx)), each=nrow(mx))
)
sum_neighb_each <- function(x) {
near.ind <- cbind( # for each x, y coord, create an index of all surrounding values
rep(x[[1]] + -1:1, 3),
rep(x[[2]] + -1:1, each=3)
)
near.ind.val <- near.ind[ # eliminate out of bound values, or the actual x,y coord itself
!(
near.ind[, 1] < 1 | near.ind[, 1] > nrow(mx) |
near.ind[, 2] < 1 | near.ind[, 2] > ncol(mx) |
(near.ind[, 1] == x[[1]] & near.ind[, 2] == x[[2]])
),
]
sum(mx[near.ind.val]) # Now sum the surrounding cell values
}
`dim<-`( # this is just to return in same matrix format as input
sapply(
split(mx.ind, row(mx.ind)), # For each x, y coordinate in input mx
sum_neighb_each # compute the neighbor sum
),
c(nrow(mx), ncol(mx)) # dimensions of input
)
}
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