# Mapreduce, pass extra arguments to reduce/vcat of DataFrames

**URL:** <https://discourse.julialang.org/t/mapreduce-pass-extra-arguments-to-reduce-vcat-of-dataframes/77347>\
**Category:** General Usage\
**Tags:** dataframes\
**Created:** [March 3, 2022, 11:02am UTC](https://discourse.julialang.org/t/mapreduce-pass-extra-arguments-to-reduce-vcat-of-dataframes/77347 "2022-03-03T11:02:01Z")\
**Posts on this page:** 1\
**Showing post:** 9

<div class="post-metadata">

**Author:** ![baptnz](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/baptnz/32/24519_2.png) [@baptnz](https://discourse.julialang.org/u/baptnz)\
**Post date:** [March 3, 2022, 4:22pm UTC](https://discourse.julialang.org/t/mapreduce-pass-extra-arguments-to-reduce-vcat-of-dataframes/77347/9 "2022-03-03T16:22:15Z")

</div>

> [@pdeffebach](#):
>
> You can also use an anonymous. They work just like in R
> 
> ```julia
> reduce((a, b) -> ..., dfs)
> 
> ```
> 
> but it looks like this doesn’t work

I’m also a bit puzzled by this; I thought I’d managed to get it to work with

```julia
mapreduce(f, (x,y) -> vcat(x,y, source="id", cols=:intersect), ps)

```

but [on my longer example](https://discourse.julialang.org/t/map-over-combinations-of-parameters-and-grouping-results-as-dataframe/77306/10) I get some unexpected `missing` values that I don’t understand at all.

---

_[View the full topic](https://discourse.julialang.org/t/mapreduce-pass-extra-arguments-to-reduce-vcat-of-dataframes/77347)._