# Parse string as tuple

**URL:** <https://discourse.julialang.org/t/parse-string-as-tuple/65244>\
**Category:** New to Julia\
**Tags:** tuple, convert, parsing\
**Created:** [July 24, 2021, 7:01pm UTC](https://discourse.julialang.org/t/parse-string-as-tuple/65244 "2021-07-24T19:01:04Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![mjanun](https://avatars.discourse-cdn.com/v4/letter/m/c4cdca/32.png) [@mjanun](https://discourse.julialang.org/u/mjanun)\
**Post date:** [July 24, 2021, 7:01pm UTC](https://discourse.julialang.org/t/parse-string-as-tuple/65244/1 "2021-07-24T19:01:04Z")

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I am trying to write a function that converts a string to a tuple. This is my code:  
`parsetuple(p::String) = Tuple(Float64(x) for x in p)`

This code can convert a string or a vector of string type to a tuple, but this doesn’t work for the example below. How can I convert `A` as shown below in to a tuple?  
This requires recognising the `,` separater is defining a vector.  
`A = "[1.1,2.2]"` or if A was instead given as `A = "1.1,2.2" `

The reason the above function will fail is that it will recognise A as one string and not a vector. The value for A is being passed as argument from the command line so by default it recognises everything as string.

How can I make my function flexible to be able to return a tuple when input is given as e.g. by  
`A = "1.1"` or `A = "[1.1,2.2]"`?

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<div class="post-metadata">

**Author:** ![stevengj](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/stevengj/32/71_2.png) [@stevengj](https://discourse.julialang.org/u/stevengj)\
**Post date:** [July 24, 2021, 8:18pm UTC](https://discourse.julialang.org/t/parse-string-as-tuple/65244/2 "2021-07-24T20:18:14Z")

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> [@mjanun](#):
>
> parsetuple(p::String) = Tuple(Float64(x) for x in p)

This is converting each _character_ in the string `p` to a `Float64` (using the numeric value of the character’s Unicode codepoint), which sounds like it is not what you want.

Of course, there are many ways to do what you want, e.g.

```julia
parsetuple(s::AbstractString) = Tuple(parse.(Float64, split(s, ',')))

```

will work on comma-delimited strings like `"1.1, 2.2"`. If you want to handle brackets too you’ll need to work a little harder to strip those off.

What is the context here? Why are you passing around small tuples of numbers in string form?

PS. A tuple may be a poor choice of data structure in a context like this where the length is determined at runtime. Normally one would use an array in such cases.

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<div class="post-metadata">

**Author:** ![rafael.guerra](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rafael.guerra/32/216610_2.png) [@rafael.guerra](https://discourse.julialang.org/u/rafael.guerra)\
**Post date:** [July 24, 2021, 9:43pm UTC](https://discourse.julialang.org/t/parse-string-as-tuple/65244/3 "2021-07-24T21:43:45Z")

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For string input from the terminal, what about:

```julia
print("Enter a number or array: ")
A = eval(Meta.parse(readline()))

```

And if one needs a tuple, then add:  
`Tuple(A)`

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<div class="post-metadata">

**Author:** ![stevengj](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/stevengj/32/71_2.png) [@stevengj](https://discourse.julialang.org/u/stevengj)\
**Post date:** [July 24, 2021, 9:51pm UTC](https://discourse.julialang.org/t/parse-string-as-tuple/65244/4 "2021-07-24T21:51:21Z")

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> [@rafael.guerra](#):
>
> `eval(Meta.parse`

I’m usually wary of using `eval` directly on user inputs, because it could execute arbitrary code. In some contexts the user is trusted, of course.

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<div class="post-metadata">

**Author:** ![rafael.guerra](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rafael.guerra/32/216610_2.png) [@rafael.guerra](https://discourse.julialang.org/u/rafael.guerra)\
**Post date:** [July 24, 2021, 9:52pm UTC](https://discourse.julialang.org/t/parse-string-as-tuple/65244/5 "2021-07-24T21:52:40Z")

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In my case, the greatest danger is myself 🙂

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<div class="post-metadata">

**Author:** ![mjanun](https://avatars.discourse-cdn.com/v4/letter/m/c4cdca/32.png) [@mjanun](https://discourse.julialang.org/u/mjanun)\
**Post date:** [July 24, 2021, 10:34pm UTC](https://discourse.julialang.org/t/parse-string-as-tuple/65244/6 "2021-07-24T22:34:10Z")

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Thank you. I have slightly modified your answer to:  
`parsetuple(s::AbstractString) = occursin(",",s) ? Tuple(parse.(Float64, split(s, ','))) : parse(Float64,s)`

> [@stevengj](#):
>
> What is the context here? Why are you passing around small tuples of numbers in string form?
> 
> PS. A tuple may be a poor choice of data structure in a context like this where the length is determined at runtime. Normally one would use an array in such cases.

I have a function with two methods;

1. `function compute(a,b,c::Tuple{Float64,Float64})`
2. `function compute(a,b,c::Float64)`

The second function expects a single value for the variable c, and the first a tuple. The length of the tuple is 2.

The reason I am passing tuples of numbers in string form is because when I call Julia from Excel using the Shell command, all the arguments are passed as strings by default and I have to convert numerical arguments to Float64 or Int64 as appropriate.

In the main Julia function that runs the whole code, e.g. I put the following lines:  
`file1 = ARGS[1]; var_b = ARGS[2]; t = parse(Float64,ARGS[3])`  
before calling that function.

Is there a better way of parsing these arguments, (e.g., so as to avoid conversion from strings to numbers)?