On Tue, Nov 3, 2015 at 8:40 AM, <[email protected]> wrote:
> I can't work out the syntax for creating symbols and assigning values to the
> variables in a loop. Here's a simple example:
You can only do this in global scope and you need to do this with
`eval`. (Since you are basically creating an expression at runtime to
execute).
This works.
```
julia> for n in 1:10
@eval $(symbol("x_$n")) = $n
end
julia> x_1
1
julia> x_10
10
```
If you want to do this in local scope, you can either use macro or
other metaprogramming techinques to construct the entire function
body.
e.g. a twisted way to return a tuple from 1 to 10 is
```
julia> @eval function f()
$([:($(symbol("x_$i")) = $i) for i in 1:10]...)
($([symbol("x_$i") for i in 1:10]...),)
end
f (generic function with 1 method)
julia> f()
(1,2,3,4,5,6,7,8,9,10)
```
Alternatively, you can check out the `@nexpr` and related macro[1].
[1] http://julia.readthedocs.org/en/latest/devdocs/cartesian/
>
> Starting with this basic idea:
>
> julia> for n in 1:10
> println("x_$(n)")
> end
>
> I'd like to do this:
>
> julia> for n in 1:10
> symbol("x_$(n)") = n
> end
> ERROR: syntax: "(string #<julia: "x_"> n)" is not a valid function
> argument name
>
> to create variables called x_1, x_2, and assign numeric values to them...
> (Numbers in this example, but will be image data eventually.)
>
> Also, for better formatting for variable names:
>
> julia> "x_$(@sprintf "%03d" 2)"
> "x_002"
>
> but this gives a similar error when used with symbol():
>
> julia> for n in 1:10
> symbol("x_$(@sprintf "%03d" 2)") = n
> end
>
> ERROR: syntax: "(string #<julia: "x_"> (let (block (= #21#out (call (.
> #0=#<julia: Base.Printf> (inert IOBuffer)))) (= #22###x#6979 2) (local
> #27#neg #26#pt #25#len #20#exp #23#do_out #24#args) (if (call (. #0# (inert
> isfinite)) #22###x#6979) (block (= (tuple
> #23#do_out #24#args) (call (. #0# (inert decode_dec)) #21#out
> #22###x#6979 #<julia: "0"> 2 -1 #<julia: Char(0x00000064)>)) (if #23#do_out
> (block (= (tuple #25#len #26#pt #27#neg) #24#args) (&& #27#neg (call (. #0#
> (inert write)) #21#out #<julia:
> Char(0x0000002d)>)) (&& (comparison (call (. #0# (inert -)) (call (. #0#
> (inert -)) 2 #27#neg) #26#pt) (. #0# (inert >)) 0) (call (. #0# (inert
> write)) #21#out #<julia: Char(0x00000030)>)) (call (. #0# (inert write))
> #21#out (call (. #0# (inert pointer)) (. #0# (inert DIGITS)))
> #26#pt)))) (call (. #0# (inert write)) #21#out (block (line 145
> printf.jl) (if (call (. #0# (inert isnan)) #22###x#6979) #<julia: "NaN"> (if
> (comparison #22###x#6979 (. #0# (inert <)) 0) #<julia: "-Inf"> #<julia:
> "Inf">))))) (. #0# (inert nothing)) (call (. #0# (inert takebuf_string))
> #21#out))))" is not a valid function argument name
>
> Perhaps `symbol` isn't what I want here?
>
