How to approach loop with increasing variable name in R - r

Question

My dataset is currently a set of answers to twenty questions with 300 observations.
Each of the questions are labled q1, q2, q3, etc.
Each observation gives a 1 to 10 response.
The code below is what I have. What I want is for the q1 to change when the counter changes in R.
totaltenq1 <- sum(UpdatedQualtrix$tenq1)
totalnineq1 <- sum(UpdatedQualtrix$nineq1)
totaleightq1 <- sum(UpdatedQualtrix$eightq1)
totalsevenq1 <- sum(UpdatedQualtrix$sevenq1)
totalsixq1 <- sum(UpdatedQualtrix$sixq1)
totalfiveq1 <- sum(UpdatedQualtrix$fiveq1)
totalfourq1 <- sum(UpdatedQualtrix$fourq1)
totalthreeq1 <- sum(UpdatedQualtrix$threeq1)
totaltwoq1 <- sum(UpdatedQualtrix$twoq1)
totaloneq1 <- sum(UpdatedQualtrix$oneq1)
totaltenq2 <- sum(UpdatedQualtrix$tenq2)
totalnineq2 <- sum(UpdatedQualtrix$nineq2)
totaleightq2 <- sum(UpdatedQualtrix$eightq2)
totalsevenq2 <- sum(UpdatedQualtrix$sevenq2)
totalsixq2 <- sum(UpdatedQualtrix$sixq2)
totalfiveq2 <- sum(UpdatedQualtrix$fiveq2)
totalfourq2 <- sum(UpdatedQualtrix$fourq2)
totalthreeq2 <- sum(UpdatedQualtrix$threeq2)
totaltwoq2 <- sum(UpdatedQualtrix$twoq2)
totaloneq2 <- sum(UpdatedQualtrix$oneq2)
I would like to have code that is
count = 20
for (i in 1:count){
totaltenq(i) <- sum(UpdatedQualtrix$tenq(i)
totalninq(I) <- sum(UpdatedQuatlrix$nineq(I)
etc
}
That way, when I do it again in the future, I can tell R how many questions it has the next time and it will change it. That way I don't have 10,000 lines of code from copying and pasting my code 20 times.

Answer 1

I don't think you need any loops at all. It just all depends on how you want to store those value. I'm a big fan of not having more variables than necessary.
Here's some sample data. I'll just make 10 rows (observations) with values 1-5.
set.seed(15)
Q<-3
numbs<-c("one","two","three","four","five","six","seven","eight","nine","ten")
qs<-paste0("q",1:Q)
qnumbs <- outer(numbs, qs, paste0)
UpdatedQualtrix <-data.frame(ID=1:10,
matrix(sample(1:5, 10*length(numbs)*Q, replace=T), nrow=10))
colnames(UpdatedQualtrix) <- c("ID",qnumbs)
Now I can sum up each of the columns with
( Qsums<-colSums(UpdatedQualtrix[, qnumbs]) )
# oneq1 twoq1 threeq1 fourq1 fiveq1 sixq1 sevenq1 eightq1 nineq1 tenq1
# 37 35 29 26 32 39 40 33 40 26
# oneq2 twoq2 threeq2 fourq2 fiveq2 sixq2 sevenq2 eightq2 nineq2 tenq2
# 37 31 19 29 25 38 36 35 28 27
# oneq3 twoq3 threeq3 fourq3 fiveq3 sixq3 sevenq3 eightq3 nineq3 tenq3
# 37 30 31 31 24 31 29 31 25 41
And if we want the totals per question we can do
sapply(qs, function(a, b) sum(Qsums[paste0(b,a)]), b=numbs)
# q1 q2 q3
# 337 305 310
Or if we want the counts per response we can do
sapply(numbs, function(a, b) sum(Qsums[paste0(a,b)]), b=qs)
# one two three four five six seven eight nine ten
# 111 96 79 86 81 108 105 99 93 94
You might want to also consider melting your data since it's so structured. You can use the reshape2 library to help. You can do
require(reshape2)
mm <- melt(UpdatedQualtrix, id.vars="ID")
mm <- cbind(mm[,-2], colsplit(mm$variable, "q", c("resp","q")))
mm$resp <- factor(mm$resp, levels=numbs)
to turn your data into a "tall" format so each value has it's own row with a column for ID, value, response and question.
str(mm)
# 'data.frame': 300 obs. of 4 variables:
# $ ID : int 1 2 3 4 5 6 7 8 9 10 ...
# $ value: int 4 1 5 4 2 5 5 2 4 5 ...
# $ resp : Factor w/ 10 levels "one","two","three",..: 1 1 1 1 1 1 1 1 1 1 ...
# $ q : int 1 1 1 1 1 1 1 1 1 1 ...
And then we can more easily do other calculations. Of you want the total scores by question, you could do
aggregate(value~q, mm, sum)
# q value
# 1 1 337
# 2 2 305
# 3 3 310
If you wanted the average value for each question/response you could do
with(mm, tapply(value, list(q,resp), mean))
# one two three four five six seven eight nine ten
# 1 3.7 3.5 2.9 2.6 3.2 3.9 4.0 3.3 4.0 2.6
# 2 3.7 3.1 1.9 2.9 2.5 3.8 3.6 3.5 2.8 2.7
# 3 3.7 3.0 3.1 3.1 2.4 3.1 2.9 3.1 2.5 4.1