Thank you - I will try this solution as well.
Sent via DROID X
-----Original message-----
From: Petr PIKAL<petr.pi...@precheza.cz>
To: David Herzberg<dav...@wpspublish.com>
Cc: Adrienne Wootten<amwoo...@ncsu.edu>,
"r-help@r-project.org"<r-help@r-project.org>
Sent: Tue, Oct 26, 2010 06:43:09 GMT+00:00
Subject: Re: [R] Conditional looping over a set of variables in R
Hi
r-help-boun...@r-project.org napsal dne 25.10.2010 20:41:55:
Adrienne, there's one glitch when I implement your solution below. When
the
loop encounters a case with no data at all (that is, all 140 item
responses
are missing), it aborts and prints this error message: " ERROR: argument
is
of length zero".
I wonder if there's a logical condition I could add that would enable R
to
skip these empty cases and continue executing on the next case that
contains data.
Thanks, Dave
David S. Herzberg, Ph.D.
Vice President, Research and Development
Western Psychological Services
12031 Wilshire Blvd.
Los Angeles, CA 90025-1251
Phone: (310)478-2061 x144
FAX: (310)478-7838
email: dav...@wpspublish.com
From: wootten.adrie...@gmail.com [mailto:wootten.adrie...@gmail.com] On
Behalf
Of Adrienne Wootten
Sent: Friday, October 22, 2010 9:09 AM
To: David Herzberg
Cc: r-help@r-project.org
Subject: Re: [R] Conditional looping over a set of variables in R
David,
here I'm referring to your data as testmat, a matrix of 140 columns and
1500
rows, but the same or similar notation can be applied to data frames in
R. If
I understand correctly, you are looking for the first response (column)
where
you got a value of 1. I'm assuming also that since your missing values
are
characters then your two numeric values are also characters. keeping
all this
in mind, try something like this.
If you really only want to know which column in each row has first
occurrence of 1 (or any other value) you can get rid of looping and use
other R capabilities.
set.seed(111)
mat<-matrix(sample(1:3, 20, replace=T),5,4)
mat
[,1] [,2] [,3] [,4]
[1,] 2 2 2 2
[2,] 3 1 2 1
[3,] 2 2 1 3
[4,] 2 2 1 1
[5,] 2 1 1 2
mat.w<-which(mat==1, arr.ind=T)
tapply(mat.w[,2], mat.w[,1], min)
2 3 4 5
2 3 3 2
mat[2, ]<-NA
mat
[,1] [,2] [,3] [,4]
[1,] 2 2 2 2
[2,] NA NA NA NA
[3,] 2 2 1 3
[4,] 2 2 1 1
[5,] 2 1 1 2
and this approach smoothly works with NA values too
mat.w<-which(mat==1, arr.ind=T)
tapply(mat.w[,2], mat.w[,1], min)
3 4 5
3 3 2
You can then use modify such output as you have info about columns and
rows. I am sure there are other maybe better options, e.g.
lll<-as.list(as.data.frame(t(mat)))
unlist(lapply(lll, function(x) min(which(x==1))))
V1 V2 V3 V4 V5
Inf Inf 3 3 2
Regards
Petr
first = c() # your extra variable which will eventually contain the
first
correct response for each case
for(i in 1:nrow(testmat)){
c = 1
while( c<=ncol(testmat) | testmat[i,c] != "1" ){
if( testmat[i,c] == "1"){
first[i] = c
break # will exit the while loop once it finds the first correct answer,
and
then jump to the next case
} else {
c=c+1 # procede to the next column if not
}
}
}
Hope this helps you out a bit.
Adrienne Wootten
NCSU
On Fri, Oct 22, 2010 at 11:33 AM, David Herzberg<dav...@wpspublish.com<
mailto:dav...@wpspublish.com>> wrote:
Here's the problem I'm trying to solve in R: I have a data frame that
consists
of about 1500 cases (rows) of data from kids who took a test of
listening
comprehension. The columns are their scores (1 = correct, 0 = incorrect,
. =
missing) on 140 test items. The items are numbered sequentially and are
ordered by increasing difficulty as you go from left to right across the
columns. I want R to go through the data and find the first correct
response
for each case. Because of basal and ceiling rules, many cases have
missing
data on many items before the first correct response appears.
For each case, I want R to evaluate the item responses sequentially
starting
with item 1. If the score is 0 or missing, proceed to the next item and
evaluate it. If the score is 1, stop the operation for that case, record
the
item number of that first correct response in a new variable, proceed to
the
next case, and restart the operation.
In SPSS, this operation would be carried out with LOOP, VECTOR, and DO
IF, as
follows (assuming the data set is already loaded):
* DECLARE A NEW VARIABLE TO HOLD THE ITEM NUMBER OF THE FIRST CORRECT
RESPONSE, SET IT EQUAL TO 0.
numeric LCfirst1.
comp LCfirst1 = 0
* DECLARE A VECTOR TO HOLD THE 140 ITEM RESPONSE VARIABLES.
vector x=LC1a_score to LC140a_score.
* SET UP A LOOP THAT WILL RUN FROM 1 TO 140, AS LONG AS LCfirst1 = 0.
"#i" IS
AN INDEX VARIABLE THAT INCREASES BY 1 EACH TIME THE LOOP RUNS.
loop #i=1 to 140 if (LCfirst1 = 0).
* SET UP A CONDITIONAL TRANSFORMATION THAT IS EVALUATED FOR EACH ELEMENT
OF
THE VE
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