Kelly,
How can I write a fundction that calculates the change between successive
observations of 10 elements of this variable? Ie. Assume the data is
sorted by date, decending. The first observation is
(Var1[_n] -Var1[_n+10])/Var[_n+10], the second observation is
(Var1[_n+2]-Var1[_n+11])/Var1[_n+11], and so on...Is this an instance
where I can use the -rolling- command? If so, how?
local i=10
while `i'<_N { //"_N" is the number of observations
replace myvar = (Var[_n]-Var[_n+`i'])/Var[_n+`i']) if _n=(`i'-9)
local i=`i'+1
}
(2) Now suppose I want to do this same calculation across say, a hundred
variables Var1-Var100. How can I loop across the variables in an efficiant
manner?
if they have a common prefix e.g. var1, var2,...var100
foreach v of var* {
local i=10
while `i'<_N { //"_N" is the number of observations
replace myvar = (`v'[_n]-`v'[_n+`i'])/`v'[_n+`i']) if _n=(`i'-9)
local i=`i'+1
}
}
If they have different names then see:
http://www.stata.com/statalist/archive/2005-08/msg00081.html
(3) A more general type of loop: suppose I have 100 variables, and I want
to display the mean and std. Deviation of each varible.
Once you have all your variable names in a local macro (vaslist) or if they
have a common prefix you can simply:
foreach v in local varlist {
sum `v'
}
I hope this helps,
Rafa
________________________
R.E. De Hoyos
Faculty of Economics
University of Cambridge
CB3 9DE, UK
www.econ.cam.ac.uk/phd/red29/
----- Original Message -----
From: "kelly johnson" <[email protected]>
To: <[email protected]>
Sent: Tuesday, August 09, 2005 1:05 PM
Subject: st: Looping questions
Hi,
I can do all of this interactively, but need help writing loops.
(1) Suppose I have a variable, say Var1
How can I write a fundction that calculates the change between successive
observations of 10 elements of this variable? Ie. Assume the data is
sorted by date, decending. The first observation is
(Var1[_n] -Var1[_n+10])/Var[_n+10], the second observation is
(Var1[_n+2]-Var1[_n+11])/Var1[_n+11], and so on...Is this an instance
where I can use the -rolling- command? If so, how?
(2) Now suppose I want to do this same calculation across say, a hundred
variables Var1-Var100. How can I loop across the variables in an efficiant
manner?
(3) A more general type of loop: suppose I have 100 variables, and I want
to display the mean and std. Deviation of each varible.
Any help will be greatly appreciated. Please be specific regarding the
coding!
Thanks,
kj
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