[R] How to perform arithmetic across rows

[Joshua Wiley]

Hi Nick,

Take a look at ?cbind and ?"["

Here is some (untested) code that is how I might go about it.  It
takes advantage of the fact that a single value will be recycled to
equal the necessary length.  Then I just assign over the NA in row 24.

myframe <- cbind(myframe, New = NA)
myframe[24, "New"] <- with(myframe, A[1] - A[24])

New will be an all NA column except for row 24.

Cheers,

Josh

On Thu, Oct 28, 2010 at 11:47 AM, Nick Ackerman <nick.ackerman at pgn.com> wrote:
>
> Hi All,
>
> I have a data frame (myframe) with variables (columns) A,B,C and 100 records
> (rows) for each. Column A is numeric. I would like to append a column to
> myframe that subtracts the value in row 24 of A from row 1 of A. In this
> procedure the first 23 rows of the new column will necessarily be blank
> (NA). Can anyone provide guidance for me here?
>
> Thanks in advance for your time.
>
> Nick
> --
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-- 
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
http://www.joshuawiley.com/