# Using . on a function where one of the parameters should not be iterated

**URL:** <https://discourse.julialang.org/t/using-on-a-function-where-one-of-the-parameters-should-not-be-iterated/102384>\
**Category:** New to Julia\
**Created:** [August 2, 2023, 8:25am UTC](https://discourse.julialang.org/t/using-on-a-function-where-one-of-the-parameters-should-not-be-iterated/102384 "2023-08-02T08:25:11Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![stefkuypers](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/stefkuypers/32/19185_2.png) [@stefkuypers](https://discourse.julialang.org/u/stefkuypers)\
**Post date:** [August 2, 2023, 8:25am UTC](https://discourse.julialang.org/t/using-on-a-function-where-one-of-the-parameters-should-not-be-iterated/102384/1 "2023-08-02T08:25:11Z")

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I’m trying to do the following. I have a function foo(x, d::DataFrame) and a 1 dimensional array a of data for which I want to call the function for each element. Problem is I want to pass a DataFrame df too but when I execute:

`.foo(a, df)`

It’s not the dataframe that is used but, logically, the elements in the dataframe.

I tried to work around this by creating a one dimensional array as follows:

```julia
dfa = Array{DataFrame}(undef, 1, length(a))
dfa .= df

```

But then I get the following error upon assignment:  
`ERROR: DimensionMismatch: array could not be broadcast to match destination`

When I do the same with an Integer type

```julia
ia = Array{Integer}(undef, 1, length(a))
ia .= 2

```

everything works just fine.

So why does the same type of code raise an error when the type is a DataFrame???

Optionally, is there a way to pass the DataFrame without putting it in an Array?

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**Author:** ![barucden](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/barucden/32/26154_2.png) [@barucden](https://discourse.julialang.org/u/barucden)\
**Post date:** [August 2, 2023, 8:33am UTC](https://discourse.julialang.org/t/using-on-a-function-where-one-of-the-parameters-should-not-be-iterated/102384/2 "2023-08-02T08:33:10Z")

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When you have a function `f(scalar, iterable)`, and you want to use broadcasting to call it for a collection of scalars and a single iterable, you need to signal that the iterable should not be broadcasted over. The standard way to do it is to wrap your iterable in `Ref`:

```julia
f(x::Integer, a::Vector) = x + length(a)

xs = [1, 2, 3, 4, 5]
a = [1, 2, 3]

julia> f.(xs, Ref(a))
5-element Vector{Int64}:
 4
 5
 6
 7
 8

```

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**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:** [August 2, 2023, 8:33am UTC](https://discourse.julialang.org/t/using-on-a-function-where-one-of-the-parameters-should-not-be-iterated/102384/3 "2023-08-02T08:33:15Z")

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If I understand correctly you just want to protect the `df` argument from broadcasting, the standard solutions are a 1-element tuple (as that doesn’t allocate) - `foo.(a, (df, ))` - or a ref: `foo.(a, Ref(df))`.