CODEWITHSUNDEEP
stata
glarys
glarys

Reputation: 131

extract value from variable stata

I have variables:

set obs 1000
g X= rnormal(0,1)
egen t=fill(1 2)

I need to generate a new variable, that would consist of one value: the first value of X. I tried:

 separate X, by(_n <= 1)

and

gen X1 = X if t<=1

But these options give me a vector 100x1 with the first value - the value I need and 99 of empty cells. How can I generate simply a one value variable:1x1?

Upvotes: 0

Views: 5136

Answers (3)

ℕʘʘḆḽḘ
ℕʘʘḆḽḘ

Reputation: 19375

you have to write two lines of codes my friend

gen X1 = X if t<=1
replace X1=X1[_n-1] if missing(X1[_n])

and

local my_parameter=X1[1]

and then you happily use your `my_parameter' macro in your arma regressions

. di `my_parameter'
-.44087866

remember, to use a macro (more usually called a parameter in other languages) in a regression in stata you need to embed its name with `'

Upvotes: 1

ander2ed
ander2ed

Reputation: 1338

I don't disagree with the other two helpful answers already posted, but when I read "How can I generate simply a one value variable:1x1?", I cant help but think you are looking for a scalar or a macro.

If that is true they you might be better off with 

sum X in 1
di r(mean)

From here, storing this value to use later is trivial:

sca MyVar = r(mean)

From help summarize, you will see that sum stores the mean, min and max among many other useful measures.

To see yourself, run return list after the call to sum to see what is returned.

By using in 1 you are restricting the summarize command to only run for the first observation. Naturally then, many of the scalars returned by summarize will equal the value you desire.

If you wish, you may also precede sum with quietly to suppress the output, or add the meanonly option to calculate only the mean along with suppressing the display.

Upvotes: 1

user4690969
user4690969

Reputation:

Perhaps this will point you in a helpful direction

generate X1 = X[1]

The point is that X[1] is the value of X in the first observation. Now having said that, what do you want to do with that value? Your dataset has 1000 observations. Do you want a local or global macro? A scalar? If you intend to use it in a formula applied to all 1000 observations, then perhaps a variable with the same value for every observation will be sufficient.

Upvotes: 0

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