R help - Apr 2010 - Using a Data Frame/Matrix outside a function

I have code that creates the same matrices , "a" and "b".
The code creating
"a" is not in a function and the code creating "b" is in a
function. I would
like to do operations on "b" like I can on "a", however I
can't figure out
how I can return a matrix (or data frame) from a function. Thanks for your
help!
> r <- 5; c <- 5
> a <- matrix(NA,nrow=5, ncol=5)
>    for(i in 1:r) {
+       for (j in 1:c) {
+          if(i==j) a[i, j] <- i 
+       }
+    }
> 
> diag(a)
[1] 1 2 3 4 5
> 
> data.out <- function(r, c) {
+    b <- matrix(NA,nrow=r, ncol=c)
+    for(i in 1:r) {
+       for (j in 1:c) {
+          if(i==j) b[i, j] <- i 
+       }
+    }
+ }
> 
> data.out(5, 5)
> diag(b)
Error in diag(b) : object 'b' not found
> 
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On Apr 1, 2010, at 12:16 PM, Greg Gilbert wrote:
>
> I have code that creates the same matrices , "a" and
"b". The code
> creating
> "a" is not in a function and the code creating "b" is
in a function.
> I would
> like to do operations on "b" like I can on "a", however
I can't
> figure out
> how I can return a matrix (or data frame) from a function. Thanks  
> for your
> help!
>
>> r <- 5; c <- 5
>> a <- matrix(NA,nrow=5, ncol=5)
>>   for(i in 1:r) {
> +       for (j in 1:c) {
> +          if(i==j) a[i, j] <- i
> +       }
> +    }
>>
>> diag(a)
> [1] 1 2 3 4 5
>>
>> data.out <- function(r, c) {
> +    b <- matrix(NA,nrow=r, ncol=c)
> +    for(i in 1:r) {
> +       for (j in 1:c) {
> +          if(i==j) b[i, j] <- i
> +       }
> +    }
> + }
>>
>> data.out(5, 5)
>> diag(b)
> Error in diag(b) : object 'b' not found
The "b" object only existed while the function was being processed. At
the conclusion of the function's activities the b object did not get  
returned as the result . Had you returned "b" or made it the last  
object evaluated (inside the function), the results of data.out(5,5)  
it would have still been accessible. Try this instead

data.out <- function(r, c) {
     b <- matrix(NA,nrow=r, ncol=c)
     for(i in 1:r) {
        for (j in 1:c) {
           if(i==j) b[i, j] <- i
        }
     }
  b}  # or equivalently return(b)

 > diag(data.out(5,5))
[1] 1 2 3 4 5


-- 
David