稀疏矩阵的colMeans乘以存储为列表的最后一个元素的矩阵

Question

我想得到最后一个列表元素的列均值，这是一个稀疏矩阵乘以一个常规矩阵。然而，每当我使用colMeans时，我都会收到错误。例如：

# Use the igraph package to create a sparse matrix
library(igraph)
my.lattice <- get.adjacency(graph.lattice(length = 5, dim = 2))

# Create a conformable matrix of TRUE and FALSE values
start <- matrix(sample(c(TRUE, FALSE), 50, replace = T), ncol = 2)

# Multiply the matrix times the vector, and save the results to a list
out <- list()
out[[1]] <- my.lattice %*% start
out[[2]] <- my.lattice %*% out[[1]]

# Try to get column means of the last element
colMeans(tail(out, 1)[[1]])  # Selecting first element because tail creates a list
# Error in colMeans(tail(out, 1)[[1]]) : 
#  'x' must be an array of at least two dimensions

# But tail(out, 1)[[1]] seems to have two dimensions
dim(tail(out, 1)[[1]])
# [1] 25  2

知道造成这个错误的原因是什么，或者我能做些什么呢？

Answer 1

看起来显式调用Matrix包中的colMeans函数有效：

> Matrix::colMeans(tail(out, 1)[[1]])
# [1] 4.48 5.48

感谢user20650提供此建议。