I can't reproduce this. The key is, or should be,
_n == 1
to restrict changes to the first record.
I did this to get a toy example:
set obs 100
egen id = seq() , to(10)
egen time = seq(), block(10)
drop if inlist(id,3,5) & time > 1
bysort id (time) : gen multiple = _N > 1
egen ID = group(id) if multiple
gen somevar = uniform()
bysort ID (time) : replace somevar = . if _n == 1 & mod(ID,5) == 0
and this works for me.
Thanks for the help on this but the procedure does not quite
do it. Or,
more precisely, it overdoes it. That is, instead of replacing with a
missing value only the entry time for the first record for
multiple-record case, it replaces all entry times with
missing values for
all records in every fifth multiple-record case. I am aiming
only the first entry time value in the first record for every fifth
--On Thursday, November 04, 2004 1:45 AM +0000 Nick Cox
> Correct. I guess the -egen- should just select those cases.
> . bysort whateverisyourid : gen multiple = _N > 1
> . egen id = group(whateverisyourid) if multiple
> . bysort id (entrytime):
> replace somevar = . if _n == 1 & mod(id,5) == 0
>> But celdjt said he wanted to do this for every fifth
>> case. He could first drop the single-record cases, apply
>> Nick's code, then
>> append them back. Or is there a neater way?
>> > Suppose your identifiers run 1, 2, ... . If this isn't true,
>> > . egen id = group(whateverisyourid)
>> > will make it so.
>> > Now, if I understand you correctly, you want to
>> > . bysort id (entrytime):
>> > replace somevar = . if _n == 1 & mod(id,5) == 0
>> > firstname.lastname@example.org
>> > > My
>> > > question is about making an adjustment to the surrogate
>> data set. The
>> > > surrogate data set contains about 3500 cases, some of which
>> > > have just one
>> > > record per case, and others have multiple records. Each
>> record has a
>> > > variable recording an entering time and an exit time for
>> that record.
>> > > Hence, single record cases have one entry time and one exit
>> > > time; multiple
>> > > record cases have multiple entry and multiple exit times. I
>> > > would like to
>> > > convert the first entry time for every fifth multiple-record
>> > > case in this
>> > > data set into a missing value. Are there any suggestions for
>> > > how this might be done.
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