Thank you Phil, this works! I had glanced at the -bysort- command beforehand, but hadn't figured to do it this way. I am especially unfamiliar with the use of the "= _n == _N" syntax though, even though I just searched for it. What does it mean...?
CM
-----Original Message-----
From: [email protected] on behalf of Philip Ryan
Sent: Tue 9/30/2003 12:22 AM
To: [email protected]
Cc:
Subject: Re: st: Short program to "collapse (# unique elements)": Use of nested loops and a "weights not allowed" message
This is a bit simpler and I think does what you want:
bysort citing nclass: gen byte unique = _n == _N
bys citing: replace unique = sum(unique)
by citing: keep if _n == _N
You should test this and maybe tweak it to deal with missing values, if
they exist in your data.
One point in your code: any command of this form "replace[_n]" will
generate an error code because Stata thinks your square brackets are
introducing weights and the syntax for -replace- does not permit
these. Also, you cannot use explicit indexing on a variable on the LHS of
a value assignment ("=") command.
Phil
At 11:41 PM 29/09/2003 -0500, you wrote:
>Hi statalisters,
>
>I have been working on a short program that doesn't seem to work, I think
>I'm just missing a small mistake... I have a data file with three
>columns: citing, cited, nclass. For every "citing", there are multiple
>"cited", and for each "cited" there is a "nclass". The file is sorted by
>citing, then nclass. I need a program to count the number of unique
>"nclass" strings associated to each "citing".
>
>As a simple example, given the following data file "data.dta":
>
>citing cited nclass
>100 20 12
>100 22 15
>100 23 15
>101 32 14
>101 33 15
>101 34 15
>101 40 17
>
>I need the following output file:
>
>citing numpatclass
>100 2 [12 and 15 are unique, 15 is repeated]
>101 3 [14, 15, 17 are unique, 15 is repeated]
>
>I have decided to do it by creating an intermediate file which I will
>later collapse(max):
>
>citing cited nclass indexpatclass
>100 20 12 1
>100 22 15 2
>100 23 15 2
>101 32 14 1
>101 33 15 2
>101 34 15 2
>101 40 17 3
>
>"indexpatclass" indexes by 1 whenever a "citing" involves a new "nclass",
>and resets to 1 whenever a new "citing" begins. So I have created a short
>program. It sorts by "citing" and "nclass", then it uses a while-loop,
>and then two if-loops. But there are two problems: (1) I am getting a
>"weights not allowed" message when I try to run it. (2) I am also not
>sure whether I am properly nesting my loops. Can anybody provide any
>insight? Or alternatively, is there a much simpler way to do what I am
>attempting?
>
>Thanks, --Chihmao.
>
>--------------------------------
>
># delimit cr
>program define uniqpatclass
>use c:\temp\data
>generate indexpatclass=0
>sort citing nclass
>replace indexpatclass=1 in 1
>generate id=_n
>
>while id<_N {
> if citing[_n]==citing[_n-1] {
> if nclass[_n]==nclass[_n-1] {
> replace indexpatclass[_n]=indexpatclass[_n-1]
> id = `id' + 1
> }
> else {
> replace indexpatclass[_n]=indexpatclass[_n-1]+1
> id = `id' + 1
> }
> }
> else {
>replace indexpatclass[_n]=1}
>id = `id' + 1
>}
>end
>
>
>
>*
>* For searches and help try:
>* http://www.stata.com/support/faqs/res/findit.html
>* http://www.stata.com/support/statalist/faq
>* http://www.ats.ucla.edu/stat/stata/
Philip Ryan
Associate Professor,
Department of Public Health
Associate Dean (Information Technology)
Faculty of Health Sciences
University of Adelaide 5005
South Australia
tel 61 8 8303 3570
fax 61 8 8223 4075
http://www.public-health.adelaide.edu.au/
CRICOS Provider Number 00123M
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