[R] matching values in a list

[dxc13]

useR's,

I want to match the real number elements of a list that has 3 matrices as
its elements and then average those numbers.  I think I am close, but I
can't get it to quite work out.  For example,

> a <- list(matrix(c(10,NA,NA,12,11,
> 10,13,NA,14,12),ncol=2),matrix(c(10,12,15,13,11,
> 13,NA,NA,12,10),ncol=2),matrix(c(10,15,NA,13,NA, 13,12,NA,NA,10),ncol=2))
> a
[[1]]
     [,1] [,2]
[1,]   10   10
[2,]   NA   13
[3,]   NA   NA
[4,]   13   14
[5,]   11   12

[[2]]
     [,1] [,2]
[1,]   10   13
[2,]   12   NA
[3,]   15   NA
[4,]   13   12
[5,]   11   10

[[3]]
     [,1] [,2]
[1,]   10   13
[2,]   15   12
[3,]   NA   NA
[4,]   13   NA
[5,]   NA   10

I want to average the non-NA numbers that simultaneously appear in each
column of all 3 matrices.  For the first column, 10 and 13 are the only
numbers that appear in all 3 matrices.  Thus, I want to take the average of
10 and 13.  Then repeat the same process for the second column.  The data
here is only a sample, but with the data I work with, there are many more
columns in each matrix in the list.  Does anyone know a efficient way to do
this?  Maybe using lapply()?  Thanks in advance.

dxc13
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