Message-ID: <37fda5350903301258u76a7bc35xebe38bb63828a130@mail.gmail.com>
Date: 2009-03-30T19:58:54Z
From: Michael Lawrence
Subject: Calculating First Occurance by a factor
In-Reply-To: <37fda5350903301235pdde136fl99ca0bc90714181f@mail.gmail.com>
I discovered Hadley Wickham's "plyr" package last week and have found
it very useful in circumstances like this:
library(plyr)
firstfixtime = ddply(
.data = data
, .variables = c('Sub','Tr','IA')
, .fun <- function(df){
df$FixTime[which.min(df$FixInx)]
}
)
> On Mon, Mar 30, 2009 at 3:40 PM, jwg20 <jason.gullifer at gmail.com> wrote:
>>
>> I'm having difficulty finding a solution to my problem that without using a
>> for loop. For the amount of data I (will) have, the for loop will probably
>> be too slow. I tried searching around before posting and couldn't find
>> anything, hopefully it's not embarrassingly easy.
>>
>> Consider the data.frame, Data, ?below
>>
>> Data
>> Sub Tr ?IA ? FixInx ?FixTime
>> p1 ? t1 ?1 ? ?1 ? ? ? ?200
>> p1 ? t1 ?2 ? ?2 ? ? ? ?350
>> p1 ? t1 ?2 ? ?3 ? ? ? ?500
>> p1 ? t1 ?3 ? ?4 ? ? ? ?600
>> p1 ? t1 ?3 ? ?5 ? ? ? ?700
>> p1 ? t1 ?4 ? ?6 ? ? ? ?850
>> p1 ? t1 ?3 ? ?7 ? ? ? ?1200
>> p1 ? t1 ?5 ? ?8 ? ? ? ?1350
>> p1 ? t1 ?5 ? ?9 ? ? ? ?1500
>>
>> What I'm trying to do is for each unique IA get the first occurring FixTime.
>> This will eventually need to be done by each Trial (Tr) and each Subject
>> Number (Sub). FixInx is essentially the number of rows in a trial. The
>> resulting data.frame is below.
>>
>> Sub Tr ?IA ?FirstFixTime
>> p1 ? t1 ?1 ? 200
>> p1 ? t1 ?2 ? 350
>> p1 ? t1 ?3 ? 600
>> p1 ? t1 ?4 ? 850
>> p1 ? t1 ?5 ? 1350
>>
>> Here is the solution I have now.
>>
>> agg = aggregate(data$FixInx, list(data$Sub, data$Tr, data$IA), min) #get the
>> minimum fix index by Sub, Tr, and IA... I can use this min fix index to pull
>> out the desired fixtime
>>
>> agg$firstfixtime = 0 # new column for results
>>
>> for (rown in 1:length(rownames(agg))){ #cycle through rows and get each
>> data$firstfixtime from FixTime in matching rows
>> ?agg$firstfixtime[rown] = as.character(data[data$Tr == agg$Group.2[rown] &
>> data$Sub == agg$Group.1[rown] & data$IA == agg$Group.3[rown] & data$FixInx
>> == agg$x[rown], ]$FixTime)
>> }
>> --
>> View this message in context: http://www.nabble.com/Calculating-First-Occurance-by-a-factor-tp22789964p22789964.html
>> Sent from the R help mailing list archive at Nabble.com.
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
--
Mike Lawrence
Graduate Student
Department of Psychology
Dalhousie University
Looking to arrange a meeting? Check my public calendar:
http://tinyurl.com/mikes-public-calendar
~ Certainty is folly... I think. ~