Bookmark and Share

Notice: On April 23, 2014, Statalist moved from an email list to a forum, based at statalist.org.


[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

st: Selecting variables corresponds to observation numbers


From   Gordon Hughes <[email protected]>
To   [email protected]
Subject   st: Selecting variables corresponds to observation numbers
Date   Sun, 06 Mar 2011 22:38:27 +0000

I would be very grateful if someone could suggest an efficient way of implementing the following task.

I have a dataset with M observations and N variables where N >> M and the variables are named var1-varN. In addition, I have an index variable ind which takes M unique values in the range 1..N. I want to select the variables that correspond to the M index values. For example, the data might be

ind  var1  var2  var3  var4  var5
2     1      2      3      4      5
4     6      7      8      9      10

so I want to create a dataset consisting of the following observations & variables

ind  var2  var4
2     2      4
4     7      9

However rather than 5 variables and 2 observations I have more like 5000 variables and 500 observations. I can do this using reshape or xpose and merging files, but this is very slow when N > 5000 and I want to repeat the exercise many times. Another alternative is to use permutation matrices in Mata, since what I am trying to do is equivalent to shuffling rows and columns in some rather large matrices. Still, I feel that there should be a cleverer way of doing it by manipulating varlists in Stata but I haven't come up with a solution.

Gordon Hughes
[email protected]

*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/


© Copyright 1996–2018 StataCorp LLC   |   Terms of use   |   Privacy   |   Contact us   |   Site index