R help - Oct 2002 - Please Help. Subtraction of Matrices?

I am just beginning to learn R.  Please help. I have two matrices. One 20 
columns by 16 rows represent student responses on a 20 question test. The 
second is 20 by 16 representing the correct responses 16 
times.  Subtracting one from the other should yield 0's if a response is 
correct.  Yet Response minus Bigkey doesn't work.  Documents indicate 
vectors should add and subtract, and seem to imply matrix algebra should 
also work.  How can I do this?  Can you help, and save me a great deal of 
time and trial-and-error.  Thanks for any help.--Gene Barlow, Ft. Lauderdale FL.


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On 10/30/02 22:58, g barlow wrote:
>I am just beginning to learn R.  Please help. I have two matrices. One 20 
>columns by 16 rows represent student responses on a 20 question test. The 
>second is 20 by 16 representing the correct responses 16 
>times.  Subtracting one from the other should yield 0's if a response is
>correct.  Yet Response minus Bigkey doesn't work.
It should work.  Look at what you get when you do it.  An error
message?  Some matrix other than what you expect?

Possibly Response or Bigkey is not actually a matrix.  Try
is.matrix(Bigkey)
is.matrix(Response)

Also try making up some data and running the same commands (with
smaller matrices perhaps).

Once you get it working, you can simplify it a bit by trasposing
Response with t() and just typing the key once, as a vector.  R
will recycle the vector column by column, e.g.

t(Response) - LittleKey

Jon
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