On 15/09/2011 10:40 AM, Jason Curole wrote:
Hi all,
I was recently writing a script to identify the value and id of the maximum
observation in a sliding window when I ran into some unexpected behavior. I
have included an example.
> test<- c()
> test$elev<- c(1:200)
> test$i<- 1
> test$window<- 10
The following works for me:
> check.max<- function(x){obs.max<- x$elev[x$i:x$i+x$window]; obs.max}
> check.max(test)
[1] 11
But then which.max doesn't seem to honor x$i+x$window:
> check.max<- function(x){obs.max<- which.max(x$elev[x$i:x$i+x$window]);
obs.max}
> check.max(test)
[1] 1
If I enclose x$i+x$window in parentheses it works:
> check.max<- function(x){obs.max<- which.max(x$elev[x$i:(x$i+x$window)]);
obs.max}
> check.max(test)
[1] 11
What am I missing?
Operator precedence. You had
x$i:x$i+x$window
but consider this:
1:1+5
The : has higher precedence than the +, so that gives 6. Yours gives
x$i+x$window
Duncan Murdoch
Here is sessionInfo (I know I need to upgrade; I am behind the state's
McAfee firewall thingy which makes it very difficult for me):
> sessionInfo()
R version 2.11.1 (2010-05-31)
x86_64-pc-linux-gnu
locale:
[1] LC_CTYPE=en_US.utf8 LC_NUMERIC=C
[3] LC_TIME=en_US.utf8 LC_COLLATE=en_US.utf8
[5] LC_MONETARY=C LC_MESSAGES=en_US.utf8
[7] LC_PAPER=en_US.utf8 LC_NAME=C
[9] LC_ADDRESS=C LC_TELEPHONE=C
[11] LC_MEASUREMENT=en_US.utf8 LC_IDENTIFICATION=C
attached base packages:
[1] stats graphics grDevices utils datasets methods base
loaded via a namespace (and not attached):
[1] tools_2.11.1
Thanks, Jason
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