Hello,
I use google docs' Forms to conduct surveys online. Multiple choices
questions are coded as comma separated values.
For example,
if the question is like:
1. What magazines do you currently subscribe to? (you can choose
multiple choices)
1) Fast Company
2) Havard Business Review
3) Business Week
4) The Economist
And if the subject chose 1) and 3), the data is coded as a cell in a
spreadsheet as,
"Fast Company, Business Week"
I read the data with read.csv into R. To analyze the data, I have to
change that string into something like flags(indicator variables?).
That is, there should be 4 variables, of which values are either 1 or
0, indicating chosen or not-chosen respectively.
Suppose the data is something like,
age favorite_magazine
1 29 Fast Company
2 31 Fast Company, Business Week
3 32 Havard Business Review, Business Week, The Economist
Then I have to chop the string in favorite_magazine column to turn
that data into something like,
age Fast Company Havard Business Review Business Week The Economist
1 29 1 0 0 0
2 31 1 0 1 0
3 32 0 1 1 1
Actually I have many more multiple choice questions in the survey.
What is the easy elegant and natural way in R to do the job?
I'd look into something like as.data.frame(lapply(strings, grep,
x=favorite_magazine, fixed=TRUE)), where strings <- c("Fast Company",
"Havard Business Review", ...).
(I take it that the mechanism is such that you can rely on at least
having everything misspelled in the same way? If it is alternatingly
"Havard" and "Harvard", then things get a bit trickier.)
--
O__ ---- Peter Dalgaard ?ster Farimagsgade 5, Entr.B
c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk) FAX: (+45) 35327907