On 30/05/2008 5:50 PM, Robert Felty wrote:
Mark,
Thanks for the reply.
hi: subset doesn't know what i is but I don't have enough knowledge
about scope to know what it's actually doing in that case. my
point is that i wouldn't put i inside a subset command and expect it to
know the value. scope is very complex in R so
doing things in the simplest manner is best like the way you do it with
49. hopfully someone else will reply with
a more detaild answer but i have a feeling that that is where your
problem lies. good luck.
I still get the wrong result without i:
Subj[1]
[1] "49"
thisSubj = subset(Trials,Trials$Subj=="49")
thisSubj$Ansr[1]
[1] "able"
thisSubj = subset(Trials,Trials$Subj==Subj[1])
thisSubj$Ansr[1]
[1] "abacus"
The problem is that I want to use this in a loop, so that I can get a score
for every subject. Maybe there is an alternative way to do this?
It's a scoping problem. To be helpful, subset looks up variables within
the dataframe first. Since it can find Subj there, that's the one it
uses in the test.
The easiest solution is just to make sure that Subj is named something
that isn't a column of Trials, e.g. localSubj. Then you could use
subset(Trials, Subj == localSubj[1])
(Notice we can skip Trials$ on the first Subj.)
If you want to write bulletproof code it's harder, because there's no
way to tell subset() *not* to look in Trials for variables. In that
case I'd avoid using subset (which is just a convenience function, and
use row indexing instead:
thisSubj <- Trials[Trials$Subj == Subj[1], ]
will give you what you expect.
Duncan Murdoch
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