Question

I am trying to get a function that is the opposite of diff() I want to add the values of adjacent columns in a matrix for each column in the matrix. I do NOT need the sum of the entire column or row. For example:

如果我说:

[ 1  2  4;
  3  5  8 ]

我最后会与:

[ 3  6;
  8  13 ]

当然,只要一两栏,这很简单,因为我可以做 x[,1,1]+x[,2],但这些矩阵相当大。

我感到惊讶的是,我似乎无法找到有效办法这样做。

Answer 1

m <- matrix(c(1,3,2,5,4,8), nrow=2)
m[,-1] + m[,-ncol(m)]

     [,1] [,2]
[1,]    3    6
[2,]    8   13

或只是为了取乐

n <- ncol(m)
x <- suppressWarnings(matrix(c(1, 1, rep(0, n-1)), 
                             nrow = n, ncol = n-1))
m %*% x

     [,1] [,2]
[1,]    3    6
[2,]    8   13

Answer 2

虚数据数据

mat <- matrix(sample(0:9, 100, replace = TRUE), nrow = 10)

解决方案 :

sum.mat <- lapply(1:(ncol(mat)-1), function(i) mat[,i] + mat[,i+1])
sum.mat <- matrix(unlist(sum.mat), byrow = FALSE, nrow = nrow(mat))

Answer 3

您可以使用:

m <- matrix(c(1,2,4,3,5,8), nrow=2, byrow=T)
sapply(2:ncol(m), function(x) m[,x] + m[,(x-1)])

友情链接