# Why does Julia think a vector is a string?

**URL:** <https://discourse.julialang.org/t/why-does-julia-think-a-vector-is-a-string/67078>\
**Category:** New to Julia\
**Created:** [August 27, 2021, 3:35am UTC](https://discourse.julialang.org/t/why-does-julia-think-a-vector-is-a-string/67078 "2021-08-27T03:35:00Z")\
**Posts on this page:** 20\
**Page:** 1

<div class="post-metadata">

**Author:** ![dgpdx](https://avatars.discourse-cdn.com/v4/letter/d/45deac/32.png) [@dgpdx](https://discourse.julialang.org/u/dgpdx)\
**Post date:** [August 27, 2021, 3:35am UTC](https://discourse.julialang.org/t/why-does-julia-think-a-vector-is-a-string/67078/1 "2021-08-27T03:35:00Z")

</div>

This works perfectly, as expected:

**julia\>** push!(S,[2,3,4])  
Stack{Any}(Deque [Any[[2, 3, 4]]])

**julia\>** push!(S,[5,6,7])  
Stack{Any}(Deque [Any[[2, 3, 4], [5, 6, 7]]])

**julia\>** x = pop()  
3-element Vector{Int64}:  
5  
6  
7

**julia\>** y = pop()  
3-element Vector{Int64}:  
2  
3  
4

**julia\>** +(x,y)  
3-element Vector{Int64}:  
7  
9  
11

But, when my program does the same thing:

**julia\>** jacli()  
S: [2,3,4]  
execute: term = [2,3,4]

S[[2,3,4]]: [4,5,6]  
execute: term = [4,5,6]

S[[2,3,4] [4,5,6]]: +  
execute: term = +

apply: x = [4,5,6] y = [2,3,4]  
**ERROR:** MethodError: no method matching +(::String, ::String)

The printout “apply: x = [4,5,6] y = [2,3,4]” is one line before the expression f(x,y) where f = +, clearly showing that x and y are vectors. Why would Julia interpret them as strings?

---

<div class="post-metadata">

**Author:** ![DNF](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dnf/32/10191_2.png) [@DNF](https://discourse.julialang.org/u/DNF)\
**Post date:** [August 27, 2021, 4:30am UTC](https://discourse.julialang.org/t/why-does-julia-think-a-vector-is-a-string/67078/3 "2021-08-27T04:30:09Z")

</div>

What is this code? Where does `S` come from? What are you popping from here

> [@dgpdx](#):
>
> **julia\>** x = pop()

?

Where does `jacli` come from?

> [@dgpdx](#):
>
> The printouts “execute:” and “apply:” are from the program during execution

What program?

This question is really confusing. Can you provide some context?

---

<div class="post-metadata">

**Author:** ![dgpdx](https://avatars.discourse-cdn.com/v4/letter/d/45deac/32.png) [@dgpdx](https://discourse.julialang.org/u/dgpdx)\
**Post date:** [August 27, 2021, 4:53am UTC](https://discourse.julialang.org/t/why-does-julia-think-a-vector-is-a-string/67078/4 "2021-08-27T04:53:27Z")

</div>

The program is jacli. S = StackAny. jacli pushes literals, like vectors, onto S and executes functions, like +, by popping the appropriate number of stack terms, then applying the function to those terms. The operation f(x,y) where f = + and x and y are vectors, fails because Julia thinks x and y are strings! But the line “apply: x = [4,5,6] y = [2,3,4]” printed at runtime, clearly shows they are not strings.

The jacli prompt shows the current stack then waits for input.

Sorry for the confusion.

---

<div class="post-metadata">

**Author:** ![kristoffer.carlsson](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kristoffer.carlsson/32/22_2.png) [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)\
**Post date:** [August 27, 2021, 5:07am UTC](https://discourse.julialang.org/t/why-does-julia-think-a-vector-is-a-string/67078/5 "2021-08-27T05:07:35Z")

</div>

You have a bug in your program but without reproducing enough of it here for us to try it out, it is impossible to say what it is.

---

<div class="post-metadata">

**Author:** ![dgpdx](https://avatars.discourse-cdn.com/v4/letter/d/45deac/32.png) [@dgpdx](https://discourse.julialang.org/u/dgpdx)\
**Post date:** [August 27, 2021, 5:11am UTC](https://discourse.julialang.org/t/why-does-julia-think-a-vector-is-a-string/67078/6 "2021-08-27T05:11:20Z")

</div>

The bug appears to be that Julia is treating vectors x and y as strings in the  
expression +(x,y).

Should I post the source code to my program, it’s rather long?

---

<div class="post-metadata">

**Author:** ![Kreiton\_Sitorus](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kreiton_sitorus/32/29268_2.png) [@Kreiton\_Sitorus](https://discourse.julialang.org/u/Kreiton_Sitorus)\
**Post date:** [August 27, 2021, 5:45am UTC](https://discourse.julialang.org/t/why-does-julia-think-a-vector-is-a-string/67078/7 "2021-08-27T05:45:21Z")

</div>

Quoting from [Please read: make it easier to help you](https://discourse.julialang.org/t/please-read-make-it-easier-to-help-you/14757). You don’t have to post whole source codes. It’s best to give us a **self-contained minimal working example** so we can reproduce your error. I believe people reading your post doesn’t understand several things:

1. the process of defining S
2. what function is pop() (because it accepts no argument) in julia we have the method pop!()
3. what function is jacli()

and it’s best to write your code in the triple-backticks. lastly, doing an addition of `Vector{Int64}` to another `Vector{Int64}` still results a `Vector{Int64}` the last time I checked.

```julia

julia> x = [1,2,3]
3-element Vector{Int64}:
 1
 2
 3

julia> y = [4,5,6]
3-element Vector{Int64}:
 4
 5
 6

julia> +(x,y)
3-element Vector{Int64}:
 5
 7
 9

```

Edit: I see you’ve edited the post @dgpdx to give an explanation, but still I haven’t yet understand what happened

---

<div class="post-metadata">

**Author:** ![dgpdx](https://avatars.discourse-cdn.com/v4/letter/d/45deac/32.png) [@dgpdx](https://discourse.julialang.org/u/dgpdx)\
**Post date:** [August 27, 2021, 5:54am UTC](https://discourse.julialang.org/t/why-does-julia-think-a-vector-is-a-string/67078/8 "2021-08-27T05:54:39Z")

</div>

What happened: my program tried f(x,y) where f = + and x an y are vectors. The program failed with the error msg: **ERROR:** MethodError: no method matching +(::String, ::String)  
The problem is that x and y were vectors not strings.

S is defined as a Julia stack of any type.

pop() uses pop!(S), but first it ensures S is not empty, printing an error msg if it is.

jacli() is the name of the running program. The line \*\*Julia jacli() should make that clear.

Here is a snippet of jacli output that shows + works fine for numeric literals, only failing for vector literals. jacl handles all literals identically.

## **julia\>** jacli() jacl version 0.1

S: 4 5.0 +  
S[9.0]: exit  
ans = 9.0

---

<div class="post-metadata">

**Author:** ![DNF](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dnf/32/10191_2.png) [@DNF](https://discourse.julialang.org/u/DNF)\
**Post date:** [August 27, 2021, 5:58am UTC](https://discourse.julialang.org/t/why-does-julia-think-a-vector-is-a-string/67078/9 "2021-08-27T05:58:46Z")

</div>

> [@dgpdx](#):
>
> The line \*\*Julia jacli() should make that clear.

I don’t know how to respond to this. Surely you must understand that the _name_ of a program you have apparently written yourself tells us nothing?

Can you copy paste from inside your function the code that defines `x` and `y` and what happens to it before the error occurs?

---

<div class="post-metadata">

**Author:** ![Kreiton\_Sitorus](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kreiton_sitorus/32/29268_2.png) [@Kreiton\_Sitorus](https://discourse.julialang.org/u/Kreiton_Sitorus)\
**Post date:** [August 27, 2021, 6:01am UTC](https://discourse.julialang.org/t/why-does-julia-think-a-vector-is-a-string/67078/10 "2021-08-27T06:01:46Z")

</div>

instead of describing it in everyday language, would you mind copy pasting your code that defines jacli()

in your IDE (or any place you write) it should be something like this:

```julia
function jacli(arguments)
    # the function jacli
end

```

and also the `pop()` function you’re talking about

```julia
function pop()
    # the function pop
end

```

---

<div class="post-metadata">

**Author:** ![GunnarFarneback](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/gunnarfarneback/32/1827_2.png) [@GunnarFarneback](https://discourse.julialang.org/u/GunnarFarneback)\
**Post date:** [August 27, 2021, 6:02am UTC](https://discourse.julialang.org/t/why-does-julia-think-a-vector-is-a-string/67078/11 "2021-08-27T06:02:24Z")

</div>

> [@Kreiton\_Sitorus](#):
>
> You don’t have to post whole source codes. It’s best to give us a **self-contained minimal working example** so we can reproduce your error.

Not only is this incredibly helpful for anyone who wants to help you. In my experience the process of extracting a minimum example frequently uncovers absolutely embarrassing bugs or thought errors which I’m thankful that I don’t have to show the world.

---

<div class="post-metadata">

**Author:** ![dgpdx](https://avatars.discourse-cdn.com/v4/letter/d/45deac/32.png) [@dgpdx](https://discourse.julialang.org/u/dgpdx)\
**Post date:** [August 27, 2021, 6:05am UTC](https://discourse.julialang.org/t/why-does-julia-think-a-vector-is-a-string/67078/12 "2021-08-27T06:05:56Z")

</div>

```julia
# Stack Operations
# ================
S = Stack{Any}()	# define the stack vector
P = Queue{Any}()	# define the program queue
 
function pop()
	if length(S) > 0
		pop!(S)
	else
		printstyled("\npop: stack underflow\n", color = :red)
	end
end

function push(x)
	push!(S,x)
end

# jacl interactive mode
# ---------------------
function jacli()
	print("\njacl version $version\n----------------")
	empty!(S)
	a = true
	while a
		prompt()		
		makeP(readline())
		a = execute()
	end
end

# execute program P
# -----------------
function execute()
	for i = 1:length(P) # process P
		term = dequeue!(P)
		if isa(term,Number) || # is it a literal?
			isa(term,Bool)   
			push!(S,term) # yes
			continue
		elseif isa(term,Function)||	# is it a function?
			term == dup ||
			term == drop ||
			term == swap ||
			term == rot ||
			term == under
			apply(term) # yes
			continue
		elseif term == "exit" # is it exit?	
			ans = pop() # quit
			println("\nans = $ans\n")
			return false
		else # must be a quotation
			push!(S,term)
		end
	end	
	return true
end 		

# Apply the function f to the stack
# (S)f = S'
# ---------------------------------
function apply(f)
	ar = methods(f).ms[1].nargs-1 # get function arity
	if ar == 0	
		if f == dup dup() end
		if f == drop drop() end
		if f == swap swap() end
		if f == rot rot() end
		if f == under under() end
	end
	if ar == 1
		x = pop()
		push(f(x))
		return
	elseif ar == 2	
		x = pop()
		y = pop()
		push(f(x,y))
		return
	elseif ar == 3
		x = pop()
		x = pop()
		z = pop()
		push(f(x,y,z)) 
	end
end

```

---

<div class="post-metadata">

**Author:** ![DNF](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dnf/32/10191_2.png) [@DNF](https://discourse.julialang.org/u/DNF)\
**Post date:** [August 27, 2021, 6:32am UTC](https://discourse.julialang.org/t/why-does-julia-think-a-vector-is-a-string/67078/13 "2021-08-27T06:32:54Z")

</div>

The code is a bit difficult to follow, using global variables like this is not recommended. The important parts probably happen inside `makeP`, which I don’t think you posted.

But I see you are using `readline` to create some data structure, so my guess is that `x` and `y` are strings from the very beginning. We need to see exactly how they are created, but this:

> [@dgpdx](#):
>
> The printout “apply: x = [4,5,6] y = [2,3,4]” is one line before the expression f(x,y) where f = +, clearly showing that x and y are vectors.

is clearly wrong, if you print the string `"[4,5,6]"` it will look like this.

---

<div class="post-metadata">

**Author:** ![mzaffalon](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mzaffalon/32/214168_2.png) [@mzaffalon](https://discourse.julialang.org/u/mzaffalon)\
**Post date:** [August 27, 2021, 6:54am UTC](https://discourse.julialang.org/t/why-does-julia-think-a-vector-is-a-string/67078/15 "2021-08-27T06:54:17Z")

</div>

Could you also place the code within three backticks, like this? It will also appear neatly indented.  
`````  
`code here`  
`````.

---

<div class="post-metadata">

**Author:** ![dgpdx](https://avatars.discourse-cdn.com/v4/letter/d/45deac/32.png) [@dgpdx](https://discourse.julialang.org/u/dgpdx)\
**Post date:** [August 27, 2021, 8:30am UTC](https://discourse.julialang.org/t/why-does-julia-think-a-vector-is-a-string/67078/16 "2021-08-27T08:30:31Z")

</div>

I think you’ve solved it. I was confused by thinking printing a string would show the quotes around it. Many thanks!

That still leaves me with a question I asked previously: how can I get [1,2,3] from “[1,2,3]”?  
It seems I can print [1,2,3], but how can I assign it to a variable?

Conversely, is there a way to read a line of input from the console other than as a string?

---

<div class="post-metadata">

**Author:** ![dgpdx](https://avatars.discourse-cdn.com/v4/letter/d/45deac/32.png) [@dgpdx](https://discourse.julialang.org/u/dgpdx)\
**Post date:** [August 27, 2021, 8:36am UTC](https://discourse.julialang.org/t/why-does-julia-think-a-vector-is-a-string/67078/17 "2021-08-27T08:36:01Z")

</div>

I’ll remember this for next time, thanks.

---

<div class="post-metadata">

**Author:** ![mzaffalon](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mzaffalon/32/214168_2.png) [@mzaffalon](https://discourse.julialang.org/u/mzaffalon)\
**Post date:** [August 27, 2021, 8:42am UTC](https://discourse.julialang.org/t/why-does-julia-think-a-vector-is-a-string/67078/18 "2021-08-27T08:42:22Z")

</div>

Maybe `parse.(Int, split(strip(str, ['[', ']']), ','))`?

---

<div class="post-metadata">

**Author:** ![mzaffalon](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mzaffalon/32/214168_2.png) [@mzaffalon](https://discourse.julialang.org/u/mzaffalon)\
**Post date:** [August 27, 2021, 8:43am UTC](https://discourse.julialang.org/t/why-does-julia-think-a-vector-is-a-string/67078/19 "2021-08-27T08:43:24Z")

</div>

No problem. Could you please edit your previous posts and apply the triple backticks? Other people may find this thread useful.

---

<div class="post-metadata">

**Author:** ![dgpdx](https://avatars.discourse-cdn.com/v4/letter/d/45deac/32.png) [@dgpdx](https://discourse.julialang.org/u/dgpdx)\
**Post date:** [August 27, 2021, 8:45am UTC](https://discourse.julialang.org/t/why-does-julia-think-a-vector-is-a-string/67078/20 "2021-08-27T08:45:43Z")

</div>

Thanks for the suggestion, but I don’t want to strip the brackets, I want to strip the quotes. I’ve tried stripping the quotes, but it doesn’t work.

---

<div class="post-metadata">

**Author:** ![dgpdx](https://avatars.discourse-cdn.com/v4/letter/d/45deac/32.png) [@dgpdx](https://discourse.julialang.org/u/dgpdx)\
**Post date:** [August 27, 2021, 8:47am UTC](https://discourse.julialang.org/t/why-does-julia-think-a-vector-is-a-string/67078/21 "2021-08-27T08:47:09Z")

</div>

Done!

---

<div class="post-metadata">

**Author:** ![mzaffalon](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mzaffalon/32/214168_2.png) [@mzaffalon](https://discourse.julialang.org/u/mzaffalon)\
**Post date:** [August 27, 2021, 8:47am UTC](https://discourse.julialang.org/t/why-does-julia-think-a-vector-is-a-string/67078/22 "2021-08-27T08:47:42Z")

</div>

The output is a vector:

```julia
julia> parse.(Int, split(strip("[1,2,3]", ['[', ']']), ','))
3-element Vector{Int64}:
 1
 2
 3

```

[Next page](https://discourse.julialang.org/t/why-does-julia-think-a-vector-is-a-string/67078.md?page=2)