R help - Jun 2004 - Recoding a multiple response question into a series of 1, 0 variables

Hello R folks.

1) The question that generated the data, which I call Qx:
Which of the following 5 items have you performed in the past month?  (multipe
response)

2) How the data is coded in my current dataframe:
The first item that a person selected is coded under a field called Qxfirst; the
second selected under Qxsecond, etc.  For the first Person, the NAs mean that
that person only selected two of the five items.

Hypothetical data is shown

                    Qxfirst    Qxsecond    Qxthird    Qxfourth    Qxfifth
Person1        4            2                NA            NA            NA
Person2        1            3                4               5               NA
Person3        3            2                NA            NA            NA

3) How I want the data to be be coded:

I want each field to be one of the five items and I want each field to contain a
1 or 0 code--1 if they mentioned the item, 0 otherwise.

Given the above data, the new fields would look as follows:

                    Item1    Item2        Item3            Item4        Item5
Person1        0            1               0                1               0  
Person2        1            0               1                1               1
Person3        0            1               1                0               0

I know how to do this using brute force (by writing bunch of ifelse statements),
but given I have quite a lot of data in the above format, I was hoping a
function would streamline this--I have tried to create a function for this, but
my efforts to date have turned up junk.

Thanks
Greg Blevins
The Market Solutions Group 




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On 06/07/04 21:28, Greg Blevins wrote:
>Hello R folks.
>
>1) The question that generated the data, which I call Qx:
>Which of the following 5 items have you performed in the past month? 
(multipe
>response)
>
>2) How the data is coded in my current dataframe:
>The first item that a person selected is coded under a field called Qxfirst;
the
>second selected under Qxsecond, etc.  For the first Person, the NAs mean
that that
>person only selected two of the five items.
>
>Hypothetical data is shown
>
>                    Qxfirst    Qxsecond    Qxthird    Qxfourth    Qxfifth
>Person1        4            2                NA            NA            NA
>Person2        1            3                4               5              
NA
>Person3        3            2                NA            NA            NA
>
>3) How I want the data to be be coded:
>
>I want each field to be one of the five items and I want each field to
contain a 1 or
>0 code--1 if they mentioned the item, 0 otherwise.
>
>Given the above data, the new fields would look as follows:
>
>                    Item1    Item2        Item3            Item4       
Item5
>Person1        0            1               0                1              
0
>Person2        1            0               1                1              
1
>Person3        0            1               1                0              
0
Here is an idea:
X <- c(4,5,NA,NA,NA) # one row
Y <- rep(NA,5) # an empty row
Y[X] <- 1

Y is now
NA NA NA 1 1
which is what you want.

So you need to do this on each row and then convert the NAs to
0s.  So first create an empty data frame, the same size as your
original one X, like my Y.  Callit Y.  Then a loop?  (I can't
think of a better way just now, like with mapply.)

for (i in [whatever]) Y[i][X[i]] <- 1

(Not tested.)  Jon
-- 
Jonathan Baron, Professor of Psychology, University of Pennsylvania
Home page:            http://www.sas.upenn.edu/~baron
R search page:        http://finzi.psych.upenn.edu/

On 06/07/04 22:45, Jonathan Baron should have written:
>for (i in [whatever]) Y[i,][X[i,]] <- 1