* 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
* Move typetraits.`$` to system. Fixes#5827.
* revive PR; adjust code to make sure everything works and add tests
* fix tests/concepts/tstackconcept.nim
* address comments
* Add the ability to sample elements from an openArray according to a parallel
array of weights/unnormalized probabilities (any sort of histogram, basically).
Also add a non-thread safe version for convenience.
* Address Araq comments on https://github.com/nim-lang/Nim/pull/10072
* import at top of file and space after '#'.
* Put in a check for non-zero total weight.
* Clarify constraint on `w`.
* Rename `rand(openArray[T])` to `sample(openArray[T])` to `sample`, deprecating
old name and name new (openArray[T], openArray[U]) variants `sample`.
* Rename caller-provided state version of rand(openArray[T]) and also clean
up doc comments.
* Add test for new non-uniform array sampler. 3 sd bound makes it 99% likely
that it will still pass in the future if the random number generator changes.
We cannot both have a tight bound to check distribution *and* loose check to
ensure resilience to RNG changes. (We cannot *guarantee* resilience, anyway.
There's always a small chance any test hits a legitimate random fluctuation.)
* Allow an escape hatch for platform specific flags (of which there are many,
for example MAP_POPULATE itself is a Linux-only thing, not other Unix).
Continue with same defaults as before in this commit, but that really
should be changed to *not* include MAP_POPULATE. While pre-faulting
all the pages can be useful sometimes *if* you know you're going to
access all the data, it is highly unlikely to be what users expect the
default to be. For some things all that up front work is 1000s of
times slower than being lazy/on-demand/only ever faulting parts of the
file. Even the MAP_POPULATE fan who originally in 2014 committed to
this file defaulted it to off (but turned it always-on as a "temporary"
work around for some long since gone/mutated compiler issue).
Anyway, at least something like this `mapFlags` gives users the ability
to override the poor default choice or activate any other idiosyncratic
platform-specific features.
* Use simple, efficient default flags, but also accept whatever the open/mapMem
caller specifies. Save flags in MemFile so they can be used in `resize`.
This field should not need exporting like the others -- callers can always
save whatever values they pass -- but we include a cautionary comment in
case anyone ever asks for a `*` there, as well as for documentation.
Also make documentation for ``mapFlags`` in open more likely to inspire care.
