[R] turning comma separated string from multiple choices into flags

[June Kim]

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,

> survey1
  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,

> survey1transformed
  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?