[R] About calculating average values from several matrices

[lily li]

Hi R users,

I have a question about manipulating the data.
For example, there are several such data frames or matrices, and I want to
calculate the average value from all the data frames or matrices. How to do
it? Also, should I convert them to data frame or matrix first? Right now,
when I use typeof() function, each one is a list.

file1
            jan   feb   mar   apr   may   jun   jul   aug   sep   oct   nov

app1   1.1   1.2    0.8    0.9   1.3    1.5   2.2   3.2   3.0    1.2   1.1
app2   3.1   3.2    2.8    2.5   2.3    2.5   3.2   3.0   2.9    1.8   1.8
app3   5.1   5.2    3.8    4.9   5.3    5.5   5.2   4.2   5.0    4.2   4.1

file2
            jan   feb   mar   apr   may   jun   jul   aug   sep   oct   nov

app1   1.9   1.5    0.5    0.9   1.2    1.8   2.5   3.7   3.2    1.5   1.6
app2   3.5   3.7    2.3    2.2   2.5    2.0   3.6   3.2   2.8    1.2   1.4
app3   5.5   5.0    3.5    4.4   5.4    5.6   5.3   4.4   5.2    4.3   4.2

file3 has the similar structure and values...

There are eight such files, and when I use the function mean(file1, file2,
file3, ..., file8), it returns the error below. Thanks for your help.

Warning message:
In mean.default(file1, file2, file3, file4, file5, file6, file7,  :
  argument is not numeric or logical: returning NA

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