On Tue, 6 Apr 2004 13:36:32 +0000, Robin Hankin <[EMAIL PROTECTED]> wrote :
> the following caught me off-guard: > > >R> a <- matrix(1:9,3,3) >R> a[a%%2==1] %+=% 1000*(1:5) >[1] 1001 2006 3015 4028 5045 >R> a > [,1] [,2] [,3] >[1,] 1001 4 1007 >[2,] 2 1005 8 >[3,] 1003 6 1009 >R> > >Why the difference when I remove the brackets? Looks to me like an operator precedence issue. Your line is equivalent to (a[a%%2==1] %+=% 1000)*(1:5) This is described in the Language Manual, in Parser | Expressions | Infix and prefix operators (section 10.4.2 in the PDF version). The user defined %xyz% operators have precedence just above * and /. >And how is the vector that is printed in the unbracketed version determined? >(why is this printed anyway? doing "a[a%%2==1] %+=% 1000" doesnt >print anything). > >Is there a better way to code up %+=% ? Not really. You can't control operator precedence in R. Duncan Murdoch ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
