= 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 the [[Stata/Merge|merge]] command to ensure that duplicates are not created.

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

If they are known to not overlap, the [[Stata/Append|append]] command can be used instead.

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

See also the [[Stata/FrLink|frlink]] command.

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== Left Join ==

Use the `merge` command as above and select cases based on the created `_merge` variable.

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

Alternatively, try using the '''`keep(groups)`''' option.

{{{
use "left.dta"
merge 1:1 KEYVARS using "right.dta", keep(1 3)
}}}

See also the [[Stata/FrLink|frlink]] command.

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== Right Join ==

As with the left join, but the groups of interest are 2 and 3.

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== Inner Join ==

As with the left join, but only group 3 is of interest.



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CategoryRicottone