Hello,

I have a dataset with student performance on a math test.  There are
multiple cases for each student (identified by id) and the concept as a
variable.

> rtest

     id   test subject     grade    concept   correct   tested per_corr
 year
1    1   83   Mathema     8         8.2.D       1            1      100
      2011
2    1   83   Mathema     8         8.3.A       1            2       50
       2011
3    1   83   Mathema     8         8.3.B       2            2      100
      2011
4    1   83   Mathema     8         8.4          2            2      100
      2011
5    1   83   Mathema     8         8.5.A       1            2       50
       2011
6    1   83   Mathema     8         8.5.B       0            2        0
        2011
7    2   83   Mathema     8         8.2.D       1            1      100
      2011
8    2   83   Mathema     8         8.3.A       2            2      100
      2011
9    2   83   Mathema     8         8.3.B       1            2       50
     2011
10  2   83   Mathema     8         8.4          2            2      100
      2011
11  2   83   Mathema     8         8.5.A       1           2       50
     2011
12  2   83   Mathema     8         8.5.B       0           2        0
     2011


I would like to make a variable for each concept (e.g. 8.2D, 8.3.A, 8.3B)
and then put that percentage correct currently under per_corr for that
variable.

Such as

      id   test    subject     grade      8.2D      8.3.A       8.3.B
year
1    1      83   Mathema     8           100        50            100
 2011
2    2      83   Mathema     8           100       100            50
2011




Does anybody have an effcient way of doing this?

What trips me up is handling the variables such as test and subject.

Thank you,

James

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