Hello,
I want to use lag on a time variable but I have to take date into
consideration ie I don't want days to overlap ie:
I don't want my first time of today to match my last time of yeterday.
In SAS I would use :
data x;
set y;
by date tim;
previous=lag(tim);
if first.date then
do;
previous=.;
end;
run;
How can I do something similar in R? I can't find any examples anywhere.
Thank you all for your help.
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