# How to supplement a function for equality check when joining the DataFrames

**URL:** <https://discourse.julialang.org/t/how-to-supplement-a-function-for-equality-check-when-joining-the-dataframes/116666>\
**Category:** Data\
**Tags:** dataframes\
**Created:** [July 5, 2024, 2:29pm UTC](https://discourse.julialang.org/t/how-to-supplement-a-function-for-equality-check-when-joining-the-dataframes/116666 "2024-07-05T14:29:46Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Gregstrq](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/gregstrq/32/20620_2.png) [@Gregstrq](https://discourse.julialang.org/u/Gregstrq)\
**Post date:** [July 5, 2024, 2:29pm UTC](https://discourse.julialang.org/t/how-to-supplement-a-function-for-equality-check-when-joining-the-dataframes/116666/1 "2024-07-05T14:29:46Z")

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I have two DataFrames, which both contain the same key, but with different accuracies: I load two datasets, which contain the physical properties of some physical objects. The first dataset contains one subset of the properties, the second one - another subset of the properties. Of course, there is also a number of properties shared by the two datasets, which are used to uniquely identify the objects.  
The problem is, one of the these identifier quantities is rounded to the different accuracy in the two subsets. **How do I check the approximate equality when joining two DataFrames? Is it possible to supplement a function, that would be used to compare the data from two datasets?**

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**Author:** ![mthelm85](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mthelm85/32/224164_2.png) [@mthelm85](https://discourse.julialang.org/u/mthelm85)\
**Post date:** [July 5, 2024, 5:02pm UTC](https://discourse.julialang.org/t/how-to-supplement-a-function-for-equality-check-when-joining-the-dataframes/116666/2 "2024-07-05T17:02:18Z")

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One option would be to use FlexiJoins.jl

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**Author:** ![Gregstrq](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/gregstrq/32/20620_2.png) [@Gregstrq](https://discourse.julialang.org/u/Gregstrq)\
**Post date:** [July 5, 2024, 5:33pm UTC](https://discourse.julialang.org/t/how-to-supplement-a-function-for-equality-check-when-joining-the-dataframes/116666/3 "2024-07-05T17:33:28Z")

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Do you know if there is option analogous to `matchmissing` from DataFrames?