Look at Syntax on R-help apropos operators precedence A.S. ---------------------------- Alessandro Semeria Models and Simulations Laboratory Montecatini Environmental Research Center (Edison Group), Via Ciro Menotti 48, 48023 Marina di Ravenna (RA), Italy Tel. +39 544 536811 Fax. +39 544 538663 E-mail: alessandro.semeria at cramont.it
Some time ago, Peter Dalgaard made the wonderful suggestion to define
"%+=%" <- function(a,b) {eval.parent(substitute(a <- a + b)) }
Which I use (R-1.8.1) as follows:
R> a <- matrix(1:9,3,3)
R> a[a%%2==1] %+=% (1000*(1:5))
R> a
[,1] [,2] [,3]
[1,] 1001 4 4007
[2,] 2 3005 8
[3,] 2003 6 5009
R>
which is what I want. But 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?
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 %+=% ?
--
Robin Hankin
Uncertainty Analyst
Southampton Oceanography Centre
SO14 3ZH
tel +44(0)23-8059-7743
initialDOTsurname at soc.soton.ac.uk (edit in obvious way; spam precaution)
Robin Hankin <rksh <at> soc.soton.ac.uk> writes:> R> a <- matrix(1:9,3,3) > But the following caught me off-guard: > R> a <- matrix(1:9,3,3) > R> a[a%%2==1] %+=% 1000*(1:5)How about this way:> a <- matrix(1:9,3,3) > "plus<-" <- function(a,value) a+value > plus(a[a%%2==1]) <- 1000*(1:5) > a[,1] [,2] [,3] [1,] 1001 4 4007 [2,] 2 3005 8 [3,] 2003 6 5009>
Value in an internal variable of a command "function", have a look on R-help apropos "function". A.S. ---------------------------- Alessandro Semeria Models and Simulations Laboratory Montecatini Environmental Research Center (Edison Group), Via Ciro Menotti 48, 48023 Marina di Ravenna (RA), Italy Tel. +39 544 536811 Fax. +39 544 538663 E-mail: alessandro.semeria at cramont.it