R help - Aug 2012 - write.table and read.table commands

Greetings,

When I try to use the write.table command to save a matrix as a file and
then open the file with read.table, if I try to take the mean of the entire
matrix, instead each column of the matrix has its mean calculated. I have
copied and pasted an example of my code below. When I try to make the
header false with the read.table command, I am given an error message. I
would appreciate any guidance for how to average the entire matrix instead
of just the columns.

Thanks

z=matrix(1:20,4,5)
write.table(z,
file="exercise.csv",sep=",",col.names=NA,qmethod="double")
j=read.table("exercise.csv",header=T,sep=",",row.names=1)
mean(j)

  V1   V2   V3   V4   V5
 2.5  6.5 10.5 14.5 18.5
Warning message:
mean(<data.frame>) is deprecated.
 Use colMeans() or sapply(*, mean) instead.

	[[alternative HTML version deleted]]

It's because read.table returns a data frame, not a matrix. You can coerce
to a matrix with as.matrix() but you might loose information if your variables
are of different classes.

Michael

On Aug 27, 2012, at 7:07 PM, Cheryl Johnson <johnson.cheryl625 at
gmail.com> wrote:
> Greetings,
> 
> When I try to use the write.table command to save a matrix as a file and
> then open the file with read.table, if I try to take the mean of the entire
> matrix, instead each column of the matrix has its mean calculated. I have
> copied and pasted an example of my code below. When I try to make the
> header false with the read.table command, I am given an error message. I
> would appreciate any guidance for how to average the entire matrix instead
> of just the columns.
> 
> Thanks
> 
> z=matrix(1:20,4,5)
> write.table(z,
file="exercise.csv",sep=",",col.names=NA,qmethod="double")
>
j=read.table("exercise.csv",header=T,sep=",",row.names=1)
> mean(j)
> 
>  V1   V2   V3   V4   V5
> 2.5  6.5 10.5 14.5 18.5
> Warning message:
> mean(<data.frame>) is deprecated.
> Use colMeans() or sapply(*, mean) instead.
> 
>    [[alternative HTML version deleted]]
> 
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