# How to use @byrow inside @chain pipeline?

**URL:** <https://discourse.julialang.org/t/how-to-use-byrow-inside-chain-pipeline/115184>\
**Category:** Data\
**Tags:** dataframes, dataframesmeta\
**Created:** [June 4, 2024, 4:16pm UTC](https://discourse.julialang.org/t/how-to-use-byrow-inside-chain-pipeline/115184 "2024-06-04T16:16:43Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**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:** [June 4, 2024, 4:16pm UTC](https://discourse.julialang.org/t/how-to-use-byrow-inside-chain-pipeline/115184/1 "2024-06-04T16:16:43Z")

</div>

I am trying to organize a pipeline for data processing using the `@chain` macro. However, I have a problem with using `@byrow` macro inside this pipeline. I get an error saying that `@byrow` is deprecated outside of DataFramesMeta macros.

So, what is the idiomatic way around?

---

<div class="post-metadata">

**Author:** ![pdeffebach](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/pdeffebach/32/10320_2.png) [@pdeffebach](https://discourse.julialang.org/u/pdeffebach)\
**Post date:** [June 4, 2024, 4:53pm UTC](https://discourse.julialang.org/t/how-to-use-byrow-inside-chain-pipeline/115184/2 "2024-06-04T16:53:11Z")

</div>

Two solutions depending on what kind of output you want.

1. Maybe you want `@eachrow`? `@eachrow` will return a data frame. It applies an operation to each row of a data frame, potentially altering the contents of the rows. There is also a limited ability to create new columns inside `@eachrow`.

```julia
julia> df = DataFrame(a = [1, 2, 3, 4], b = ["a", "b", "c", "d"]);

julia> @eachrow df begin 
           :a = 2 * :a
       end
4×2 DataFrame
 Row │ a b      
     │ Int64 String 
─────┼───────────────
   1 │ 2 a
   2 │ 4 b
   3 │ 6 c
   4 │ 8 d

```

1. You can use `@with @byrow ...`. This returns a `vector`. Recall that

```julia
@with df :a + :b

```

is akin to

```julia
function fun(a, b)
    a + b
end
fun(df.a, df.b)

```

Adding `@byrow` just broadcasts `fun` across the columns.

```julia
@with df @byrow :a + :b

```

becomes

```julia
function fun(a, b)
    a + b
end
fun.(df.a, df.b)

```

Here it is in action

```julia
julia> using Statistics

julia> df = DataFrame(a = [1, 2, 3, 4], b = ["a", "b", "c", "d"]);

julia> @with df begin
           mean(:a) * 2
       end
5.0

julia> @with df @byrow begin
           :a + 100
       end
4-element Vector{Int64}:
 101
 102
 103
 104

```

---

<div class="post-metadata">

**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:** [June 4, 2024, 5:36pm UTC](https://discourse.julialang.org/t/how-to-use-byrow-inside-chain-pipeline/115184/3 "2024-06-04T17:36:01Z")

</div>

This is very funny. I have tried to make a minimal working example to showcase my problem, but this time I did something a little bit differently and this time it worked. Hard to tell what exactly I have changed. There was actually a mistake in the transformation function that I have tried to apply, but the error that I was getting was about `@byrow`. But now that I fixed it, I don’t get this error any more.

If you were interested, the MWE for what I was doing lookes like

```julia
using DataFrames, DataFramesMeta

df0 = DataFrame(p1 = collect(1:5), p2 = collect(6:10), p3 = [1,0,1,0,1], j=[randn(100) for i=1:5], w = [randn(100) for i=1:5])

@chain df0 begin
	@subset :p3.==1
	@select :p1 :p2 @byrow :R = 1/dot(:j,:w)
end

```