Creating variable with values extracted from a matrix

[Marine Jouvin]

Hi,

I am currently working with a database where I have about 200,000 obs.

Each observation belongs to a group identified by the variable "x_id". For each observation, I also know its status (belongs to the control or treatment group), and the date on which it took place.

Using the digdis package, I am currently using the following code to extract the MAD for obs. linked to the control group and at a specific date:

digdis x if statut ==0 & date==0, position(1) by(x_id)
matrix list r(mad)

I get the following matrix:

My variable "x_id" takes values from 0 to 208. I would like to create a variable that would take the value displayed in the matrix for (i.e.) 12, which is 3.3590708, when the variable x_id==12, and so on...

Any idea that might help ?

[George Ford]

maybe this is a start. if you want them all, I'd dump the status condition.

not sure if xsvmat allows for format definitions so you don't have to destring.

ssc install xsvmat

clear
cd S:\STATA
use auto, clear

g x_id = trunk
digdis mpg  , position(1) by(x_id)
matrix list r(mad)
matrix MAD = r(mad)'
matrix list MAD
xsvmat MAD , rowname(x_id) colname(MAD) saving(MAD.dta, replace)
use MAD, clear
destring x_id, force replace
save MAD, replace
use auto, clear
g x_id = trunk
joinby x_id using MAD

[Marine Jouvin]

Thanks a lot, it did the job !

[George Ford]

I'm sure there's a simpler way, but I leave it to you to find it. As you can, see the trick is that your join is a colname.

[George Ford]

Also note that xsvmat allows you to save the file in a frame, so you can avoid the opening and closing.