rapply

Tabulating multiple response questions


Imagine that I have a question for which there are four options, and a respondent can select zero or any combination of the four. The variables are named A, B, C, and D and the responses are stored in a data.frame as below.

set.seed(1)
dat = data.frame(A = sample(c(0, 1), 20, replace=TRUE), 
                 B = sample(c(0, 1), 20, replace=TRUE), 
                 C = sample(c(0, 1), 20, replace=TRUE),
                 D = sample(c(0, 1), 20, replace=TRUE))

I can tabulate the combination of responses (for example, how many responded with A alone, or A+B, or C+D, and so on) by doing the following:

data.frame(table(dat))
#    A B C D Freq
# 1  0 0 0 0    2
# 2  1 0 0 0    2
# 3  0 1 0 0    0
# 4  1 1 0 0    1
# 5  0 0 1 0    1
# 6  1 0 1 0    3
# 7  0 1 1 0    0
# 8  1 1 1 0    2
# 9  0 0 0 1    0
# 10 1 0 0 1    2
# 11 0 1 0 1    1
# 12 1 1 0 1    1
# 13 0 0 1 1    2
# 14 1 0 1 1    0
# 15 0 1 1 1    3
# 16 1 1 1 1    0

I would like to now create a new column that shows the letter combination that is being represented by this output. For example, row 4 represents the count of A+B responses, and row 14 represents the count of A+C+D responses.

I think that one of the apply functions would be useful here, but I'm not sure how to proceed.


Solution

  • dat.t <- data.frame(table(dat))    
    dat.t$combn <- apply(dat.t[,1:4] == 1, 1, function(x) paste(names(dat)[x], collapse=' + '))
    
    > dat.t
       A B C D Freq         combn
    1  0 0 0 0    2              
    2  1 0 0 0    2             A
    3  0 1 0 0    0             B
    4  1 1 0 0    1         A + B
    5  0 0 1 0    1             C
    6  1 0 1 0    3         A + C
    7  0 1 1 0    0         B + C
    8  1 1 1 0    2     A + B + C
    9  0 0 0 1    0             D
    10 1 0 0 1    2         A + D
    11 0 1 0 1    1         B + D
    12 1 1 0 1    1     A + B + D
    13 0 0 1 1    2         C + D
    14 1 0 1 1    0     A + C + D
    15 0 1 1 1    3     B + C + D
    16 1 1 1 1    0 A + B + C + D
    >