On 04/08/2014 02:21 PM, John Clements wrote:
On Apr 8, 2014, at 12:04 PM, John Clements <[email protected]> wrote:
On Apr 8, 2014, at 11:54 AM, Sam Tobin-Hochstadt <[email protected]> wrote:
On Tue, Apr 8, 2014 at 2:48 PM, John Clements <[email protected]> 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`.
But… in-indexed produces a sequence of 2-value elements. I guess I can get it
working with sequence-map:
(plot (lines (sequence-map (lambda (a b) (vector b a))
(in-indexed (in-array fft-maxes)))))
BUT WAIT! no, that doesn’t work in the typed setting, because sequence-map’s
type doesn’t work for 2-valued sequences. Back to square 1.
Got it… “in-values-sequence”.
John
Four more options:
(plot (lines (for/list : (Listof (List Index Real))
([js (in-array-indexes (array-shape fft-maxes))]
[x (in-array fft-maxes)])
(list (vector-ref js 0) x))))
(plot (lines (array->list
(array-map (λ ([js : Indexes] [x : Real])
(list (vector-ref js 0) x))
(indexes-array (array-shape fft-maxes))
fft-maxes))))
(plot (lines
(matrix->list*
(list-array->array
(for/array ([js (in-array-indexes (array-shape fft-maxes))]
[x (in-array fft-maxes)]) : (List Index Real)
(list (vector-ref js 0) x))
1))))
(plot (lines (matrix->list*
(array-list->array
(list (build-array (array-shape fft-maxes)
(λ ([js : Indexes])
(vector-ref js 0)))
fft-maxes)
1))))
The last two use `matrix->list*' because there's no way for TR to prove
that `array->list*' produces a (Listof (Listof t)). (Nothing about an
array's shape is part of the type.)
Neil ⊥
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