# How to reference new variables in a combine for dataframes?

**URL:** <https://discourse.julialang.org/t/how-to-reference-new-variables-in-a-combine-for-dataframes/52851>\
**Category:** General Usage\
**Tags:** dataframes\
**Created:** [January 4, 2021, 9:41pm UTC](https://discourse.julialang.org/t/how-to-reference-new-variables-in-a-combine-for-dataframes/52851 "2021-01-04T21:41:44Z")\
**Posts on this page:** 1\
**Showing post:** 5

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**Author:** ![bdeonovic](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/bdeonovic/32/3928_2.png) [@bdeonovic](https://discourse.julialang.org/u/bdeonovic)\
**Post date:** [January 6, 2021, 8:13pm UTC](https://discourse.julialang.org/t/how-to-reference-new-variables-in-a-combine-for-dataframes/52851/5 "2021-01-06T20:13:48Z")

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I ended up using the approach taken here:

> [@Dpylr do equivalent in query.jl standalone syntax?](https://discourse.julialang.org/t/dpylr-do-equivalent-in-query-jl-standalone-syntax/24745/4):
>
> Whoa cool. So what does the \_ \_ refer to on the @mapmany line? It looks like it’s the original dataframe somehow, but how does it know that that’s what you’re referring to?

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