Beginner Loop Question with dynamic variable names

j<-data.frame(q1=rnorm(10),q2=rnorm(10))
j

for(i in 1:3){j[,paste(sep="","res",i)]<-with(j,q1+q2)}
j

Dear all,

I have another small scripting-beginner problem which you hopefully can
help:

I compute new variables with:

# Question 1
results$q1 <- with(results, q1_1*1+ q1_2*2+ q1_3*3+ q1_4*4+ q1_5*5)
# Question 2
results$q2 <- with(results, q2_1*1+ q2_2*2+ q2_3*3+ q2_4*4+ q2_5*5)
# Question 3
results$q3 <- with(results, q3_1*1+ q3_2*2+ q3_3*3+ q3_4*4+ q3_5*5)
# Question 4
results$q4 <- with(results, q4_1*1+ q4_2*2+ q4_3*3+ q4_4*4+ q4_5*5)

This is very inefficient so I would like to do this in a loop like:

for (i in 1:20) {results$q1 <- with(results, q1_1*1+ q1_2*2+ q1_3*3+
q1_4*4+ q1_5*5)}

My question now:
How to replace the "1"-s (results$q1, q1_1...) in the variables with the
looping variable?

Here like I like it (just for illustration - of course I still miss the
function to tell R that it should append the value of i to the variable
name):

# i is the number of questions - just an illustration, I know it does
not work this way
for (i in 1:20) {results$qi <- with(results, qi_1*1+ qi_2*2+ qi_3*3+
qi_4*4+ qi_5*5)}

Help would be greatly appreciated. Thanks in advance.

Peter


___CURE - Center for Usability Research & Engineering___

Peter Wolkerstorfer
Usability Engineer
Hauffgasse 3-5, 1110 Wien, Austria

[Tel]  +43.1.743 54 51.46
[Fax]  +43.1.743 54 51.30

[Mail] wolkerstorfer at cure.at
[Web]  http://www.cure.at

Dear all,

I have another small scripting-beginner problem which you hopefully can
help:

I compute new variables with:

# Question 1
results$q1 <- with(results, q1_1*1+ q1_2*2+ q1_3*3+ q1_4*4+ q1_5*5)
# Question 2
results$q2 <- with(results, q2_1*1+ q2_2*2+ q2_3*3+ q2_4*4+ q2_5*5)
# Question 3
results$q3 <- with(results, q3_1*1+ q3_2*2+ q3_3*3+ q3_4*4+ q3_5*5)
# Question 4
results$q4 <- with(results, q4_1*1+ q4_2*2+ q4_3*3+ q4_4*4+ q4_5*5)

This is very inefficient so I would like to do this in a loop like:

for (i in 1:20) {results$q1 <- with(results, q1_1*1+ q1_2*2+ q1_3*3+
q1_4*4+ q1_5*5)}

My question now:
How to replace the "1"-s (results$q1, q1_1...) in the variables with the
looping variable?

Here like I like it (just for illustration - of course I still miss the
function to tell R that it should append the value of i to the variable
name):

# i is the number of questions - just an illustration, I know it does
not work this way
for (i in 1:20) {results$qi <- with(results, qi_1*1+ qi_2*2+ qi_3*3+
qi_4*4+ qi_5*5)}

Help would be greatly appreciated. Thanks in advance.

Peter


___CURE - Center for Usability Research & Engineering___

Peter Wolkerstorfer
Usability Engineer
Hauffgasse 3-5, 1110 Wien, Austria

[Tel]  +43.1.743 54 51.46
[Fax]  +43.1.743 54 51.30

[Mail] wolkerstorfer at cure.at
[Web]  http://www.cure.at

I think this does what you are looking for:

dta <- 
data.frame(q1_1=rep(1,5),q1_2=rep(2,5),q2_1=rep(3,5),q2_2=rep(4,5))

for (i in 1:2) {
   e1  <- paste("q",i,"_1 + q",i,"_2 * 2",sep="")
   assign(paste("q",i,sep=""),with(dta,eval(parse(text=e1))))
}

On 25/09/06, Peter Wolkerstorfer - CURE <wolkerstorfer at cure.at> 
wrote:

Dear all,

I have another small scripting-beginner problem which you hopefully 
can
help:

I compute new variables with:

# Question 1
results$q1 <- with(results, q1_1*1+ q1_2*2+ q1_3*3+ q1_4*4+ q1_5*5)
# Question 2
results$q2 <- with(results, q2_1*1+ q2_2*2+ q2_3*3+ q2_4*4+ q2_5*5)
# Question 3
results$q3 <- with(results, q3_1*1+ q3_2*2+ q3_3*3+ q3_4*4+ q3_5*5)
# Question 4
results$q4 <- with(results, q4_1*1+ q4_2*2+ q4_3*3+ q4_4*4+ q4_5*5)

This is very inefficient so I would like to do this in a loop like:

for (i in 1:20) {results$q1 <- with(results, q1_1*1+ q1_2*2+ 
q1_3*3+
q1_4*4+ q1_5*5)}

My question now:
How to replace the "1"-s (results$q1, q1_1...) in the variables 
with the
looping variable?

Here like I like it (just for illustration - of course I still miss 
the
function to tell R that it should append the value of i to the 
variable
name):

# i is the number of questions - just an illustration, I know it 
does
not work this way
for (i in 1:20) {results$qi <- with(results, qi_1*1+ qi_2*2+ 
qi_3*3+
qi_4*4+ qi_5*5)}

Help would be greatly appreciated. Thanks in advance.

Peter


___CURE - Center for Usability Research & Engineering___

Peter Wolkerstorfer
Usability Engineer
Hauffgasse 3-5, 1110 Wien, Austria

[Tel]  +43.1.743 54 51.46
[Fax]  +43.1.743 54 51.30

[Mail] wolkerstorfer at cure.at
[Web]  http://www.cure.at

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Said Business School
University of Oxford
Park End Street
Oxford OX1 1HP