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Resolve things raised in https://github.com/nim-lang/Nim/issues/10081 ? (#10084)

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* Resolve things raised in https://github.com/nim-lang/Nim/issues/10081 ?
CDF is a standard ident in all things related to random numbers/sampling,
and full words "cumulativeDistributionFunction" would be silly long, in
this case, IMO.  We use lowercase `cdf` to make it not look like a type,
remove all looping from `sample` letting callers do it.  Besides just
side-stepping any `sampleSize` name choice, callers may want to filter
out samples anyway which this makes slightly simpler.

Also add two variants of `cumsum`, value return and in-place update
distinguished by the var-ness of the first argument.  Add tests for
`int` and `float` for both `cumsum` and the new `sample`.  (The sample
tests exercise the value return mode of `cumsum`.)

Functionality pre-this-PR `sample(a, w)` is now the almost as simple
`for i in 0..<n: sample(a, w.cumsum)`, but this new code factoring is
almost surely better.  The statistical tests pass, as before.

* Address Araq comment in https://github.com/nim-lang/Nim/pull/10084
We can always add in some `var` version later if desired to save
memory, but this change now at least firms up the `sample` interface.

* Rename `cumsum` -> `cumsummed` to honor NEP1 style.  Re-instate `cumsum` as
the in-place transformation.  Test both in `tests/stdlib/tmath.nim` and use
`cumsummed` in the example code for sample since that's a simpler example.

* Fix requests from https://github.com/nim-lang/Nim/pull/10084 :
  example in lib/pure/math.nim and comment whitespace in lib/pure/random.nim
This commit is contained in:
c-blake 2018-12-31 08:52:51 -05:00 • committed by Andreas Rumpf
commit 7ac1fc81fd
3 changed files with 85 additions and 29 deletions
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18
lib/pure/math.nim
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@ -163,6 +163,24 @@ proc prod*[T](x: openArray[T]): T {.noSideEffect.} =
result = 1.T
for i in items(x): result = result * i
proc cumsummed*[T](x: openArray[T]): seq[T] =
## Return cumulative aka prefix summation of ``x``.
##
## .. code-block:: nim
## var x = [1, 2, 3, 4]
## echo x.cumsummed # [1, 3, 6, 10]
result.setLen(x.len)
result[0] = x[0]
for i in 1 ..< x.len: result[i] = result[i-1] + x[i]
proc cumsum*[T](x: var openArray[T]) =
## Transforms ``x`` in-place into its cumulative aka prefix summation.
##
## .. code-block:: nim
## var x = [1, 2, 3, 4]
## x.cumsum; echo x # [1, 3, 6, 10]
for i in 1 ..< x.len: x[i] = x[i-1] + x[i]
{.push noSideEffect.}
when not defined(JS): # C
proc sqrt*(x: float32): float32 {.importc: "sqrtf", header: "<math.h>".}