[datatable-help] Data table syntax

[Damian Betebenner]

Thanks for the invaluable help on my previous questions. The speed up in create summary tables has been immense and I'm enthused about all the possibilities going forward.

I'm currently stuck in trying to put together syntax for a "long" for table. In the example below, each case is a unique Student by Year combination. What I'm trying to do is take
such a table, aggregate on the student's  current year (i.e., 2009 in this data) SCHOOL_NUMBER, and calculate their mean score in the previous year (i.e., 2008 in this data).

If the file were "wide", with each case representing a unique student with separate variables for the year, then it would be easy to break on the 2009 SCHOOL_NUMBER and take the
mean of the 2008 SCORE.

Is conversion of long to wide necessary to do this?


      STUDENT_ID SCHOOL_NUMBER YEAR SCORE
 [1,]          1           100 2008    39
 [2,]          1           200 2009    48
 [3,]          2           100 2008    64
 [4,]          2           200 2009    73
 [5,]          3           100 2008    35
 [6,]          3           200 2009    35
 [7,]          4           100 2008    52
 [8,]          4           200 2009    61
 [9,]          5           100 2008    51
[10,]          5           200 2009    58
[11,]          6           300 2008    45
[12,]          6           400 2009    55
[13,]          7           300 2008    69
[14,]          7           400 2009    77
[15,]          8           300 2008    47
[16,]          8           400 2009    47
[17,]          9           300 2008    57
[18,]          9           400 2009    58
[19,]         10           300 2008    47
[20,]         10           400 2009    53


Thanks,

Damian


Damian Betebenner
Center for Assessment
PO Box 351
Dover, NH   03821-0351

Phone (office): (603) 516-7900
Phone (cell): (857) 234-2474
Fax: (603) 516-7910

dbetebenner at nciea.org<mailto:dbetebenner at nciea.org>
www.nciea.org<http://www.nciea.org/>



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