# [racket] TR+plot exposes idx9, idx54, etc?

 From: Sam Tobin-Hochstadt (samth at cs.indiana.edu) Date: Tue Apr 8 14:54:07 EDT 2014 Previous message: [racket] TR+plot exposes idx9, idx54, etc? Next message: [racket] TR+plot exposes idx9, idx54, etc? Messages sorted by: [date] [thread] [subject] [author]

```On Tue, Apr 8, 2014 at 2:48 PM, John Clements <clements at brinckerhoff.org> wrote:
> Here’s a short piece of code that tries to plot an array:
>
> #lang typed/racket
>
> (require plot
>          math/array)
>
> (define fft-maxes (array #[3.2 978.9 -2397]))
>
> (: with-indexes (Vectorof (Vector Nonnegative-Integer Real)))
> (define with-indexes
>   (for/vector : (Vectorof (Vector Nonnegative-Integer Real))
>     ([i : Nonnegative-Integer (in-naturals)]
>      [a (in-array fft-maxes)])
>     (ann (vector (ann i Nonnegative-Integer) a)
>          (Vector Nonnegative-Integer Real))))
>
>
> (plot (lines (in-vector with-indexes)))
>
> I have two questions.
> 1) Is there an easier way to pair an array with indices? This was kind of challenging.

Try `in-indexed`.

> 2) When I run this, I get
>
> Type Checker: missing type for identifier;
>  consider using `require/typed' to import it
>   identifier: idX9
>   from module: plot in: #%module-begin
> . Type Checker: missing type for identifier;
>  consider using `require/typed' to import it
>   identifier: idX54
>   from module: plot/no-gui in: #%module-begin
> . Type Checker: Summary: 2 errors encountered in:
>   #%module-begin
>   #%module-begin

These are both from the use of `in-array` and/or `fft-maxes`, not from
your for loop.  Probably the right thing is to use `plot/typed`.

Sam

```

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