R help - Oct 2011 - Trying to create a function to extract values from a matrix

My issue seems simple but I can't find any method to work...

I've got a matrix with 4 columns and I want to extract the values from each
row to make a new 2x2 matrix for each row.  From these resultant matrices, I
want to get the Eigen Values and output them from the function as usable
numbers (not a text string).

Here's the function...

###

Ef = 
function(MAT) {for(i in c(1:(length(MAT)/4))) 
return(matrix(c (eigen(matrix(c(MAT[i,]),ncol=2))$values),ncol=2))}

###

This function will return only the Eigen Values of the first row (MAT[1,])
of the matrix.  However, if I replace "return" in the function with
"cat",
the function will output all the desired values, but they will be as a text
string, which I can't use.

Furthermore, if I set a variable in the function, and then return the
variable at the end of the function, it yields the Eigen Values for the last
row of my matrix.  That function looks like...

###

Ef= 
function(MAT) {for(i in c(1:(length(MAT)/4))) 
EV=(matrix(c (eigen(matrix(c(MAT[i,]),ncol=2))$values),ncol=2)); 
return(EV)}
 
###
>From what I can tell, it seems that the function is working, however, I
don't know how to get it to spit out all the information in a usable manner.
Thanks for any suggestions.

Stephen

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This might be an easier method:

suppose your data is in MAT

t(apply(MAT, 1, function(v) eigen(matrix(v, 2))$values))

Your problem is that return() automatically returns the output and
ceases function execution as soon as its hit.

Michael

On Thu, Oct 27, 2011 at 10:44 AM, StephenHughes <kshughes at ncsu.edu>
wrote:
> My issue seems simple but I can't find any method to work...
>
> I've got a matrix with 4 columns and I want to extract the values from
each
> row to make a new 2x2 matrix for each row. ?From these resultant matrices,
I
> want to get the Eigen Values and output them from the function as usable
> numbers (not a text string).
>
> Here's the function...
>
> ###
>
> Ef > function(MAT) {for(i in c(1:(length(MAT)/4)))
> return(matrix(c (eigen(matrix(c(MAT[i,]),ncol=2))$values),ncol=2))}
>
> ###
>
> This function will return only the Eigen Values of the first row (MAT[1,])
> of the matrix. ?However, if I replace "return" in the function
with "cat",
> the function will output all the desired values, but they will be as a text
> string, which I can't use.
>
> Furthermore, if I set a variable in the function, and then return the
> variable at the end of the function, it yields the Eigen Values for the
last
> row of my matrix. ?That function looks like...
>
> ###
>
> Ef> function(MAT) {for(i in c(1:(length(MAT)/4)))
> EV=(matrix(c (eigen(matrix(c(MAT[i,]),ncol=2))$values),ncol=2));
> return(EV)}
>
> ###
>
> >From what I can tell, it seems that the function is working, however, I
> don't know how to get it to spit out all the information in a usable
manner.
> Thanks for any suggestions.
>
> Stephen
>
> --
> View this message in context:
http://r.789695.n4.nabble.com/Trying-to-create-a-function-to-extract-values-from-a-matrix-tp3944737p3944737.html
> Sent from the R help mailing list archive at Nabble.com.
>
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> PLEASE do read the posting guide
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> and provide commented, minimal, self-contained, reproducible code.
>

Thanks Michael, this worked great.

Stephen

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