# DataFrame vector to columns

**URL:** <https://discourse.julialang.org/t/dataframe-vector-to-columns/52577>\
**Category:** New to Julia\
**Tags:** dataframes\
**Created:** [December 29, 2020, 4:36pm UTC](https://discourse.julialang.org/t/dataframe-vector-to-columns/52577 "2020-12-29T16:36:51Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![ZettEff](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/zetteff/32/31976_2.png) [@ZettEff](https://discourse.julialang.org/u/ZettEff)\
**Post date:** [December 29, 2020, 4:36pm UTC](https://discourse.julialang.org/t/dataframe-vector-to-columns/52577/1 "2020-12-29T16:36:51Z")

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I tried to find a way to transform a column containing vectors (all of equal length) as values into columns per vector element.

```julia
df = DataFrame(data=rand(3), list_data=[[1, 2], [3, 4], [5, 6]])
transform(df, :list_data => (col -> [el for el in col]) => [:A,:B])

```

The above code works. However, I don’t have any clue why it is working? My understanding is that

`col`: represents column df.list\_data which is of type `Array{Array{Int64,1},1}`.

But isn’t `[el for el in col]` also of type `Array{Array{Int64,1},1}`?

At least `typeof([el for el in df.list_data]) == typeof(df.list_data)` returns true.

So why does the split into columns then work?

This may be a weird question but I want to understand the mechanics behind dataframes and julia.

Thanks!

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<div class="post-metadata">

**Author:** ![nilshg](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/nilshg/32/2283_2.png) [@nilshg](https://discourse.julialang.org/u/nilshg)\
**Post date:** [December 29, 2020, 4:44pm UTC](https://discourse.julialang.org/t/dataframe-vector-to-columns/52577/2 "2020-12-29T16:44:56Z")

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I think you might be interested in [this recent blog post](https://bkamins.github.io/julialang/2020/12/24/minilanguage.html) from Bogumil - your case is explained in the section “Multiple target columns”.

Here the elements of `list_data` are iterable (as they are vectors), so in combination with multiple return columns they are split up. Your transformation `col -> [el for el in col]` does indeed not do anything:

```julia
julia> df.list_data == [el for el in df.list_data]
true

```

and so you could have shortened your example to

```julia
julia> transform(df, :list_data => identity => [:A,:B])
3×4 DataFrame
 Row │ data list_data A B     
     │ Float64 Array… Int64 Int64 
─────┼───────────────────────────────────
   1 │ 0.895446 [1, 2] 1 2
   2 │ 0.386052 [3, 4] 3 4
   3 │ 0.978884 [5, 6] 5 6

```

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<div class="post-metadata">

**Author:** ![ZettEff](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/zetteff/32/31976_2.png) [@ZettEff](https://discourse.julialang.org/u/ZettEff)\
**Post date:** [December 29, 2020, 5:05pm UTC](https://discourse.julialang.org/t/dataframe-vector-to-columns/52577/3 "2020-12-29T17:05:34Z")

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Great, thanks for your answer. Will check out the mentioned blog.