= Joining Data with Stata =

Stata offers several commands for joining datasets. 

<<TableOfContents>>

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== Full Join ==

If the left and right datasets may overlap, use [[Stata/Merge|-merge-]] to ensure that duplicates are not created.

{{{
use "left.dta"
merge 1:1 KEYVARS using "right.dta"
}}}

If they are known to not overlap, consider using [[Stata/Append|-append-]] instead.

{{{
use "cohort1.dta"
append using "cohort2.dta"
}}}

See also [[Stata/FrLink|-frlink-]].

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== Left, Right, or Inner Joins ==

Use [[Stata/Merge|-merge-]] as above and select cases based on the automatically created `_merge` variable.

{{{
use "left.dta"
merge 1:1 KEYVARS using "right.dta"
keep if _merge==1 | _merge==3       // left join
keep if _merge==2 | _merge==3       // right join
keep if _merge==3                   // inner join
}}}



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CategoryRicottone