9.20.1 Top new questions this week

9.20.1.1 How to GroupBy or Gather on a nested association
9.20.1.2 Highlight parts of two different curves
9.20.1.3 DataStructure's "DynamicArray" underperforms Association?
9.20.1.4 How to recursively subdivide a quadrilateral?
9.20.1.5 Better Stirling Approximation Error
9.20.1.6 IntervalMarkers bands not filled for negative x values
9.20.1.7 How to set to 0 all terms in a matrix which contain a minus
9.20.1.1 How to GroupBy or Gather on a nested association

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=286524

I've been trying to figure out how to gather or group on a list of a nested associated--and flailing. 
Here is a reduced example. I'm interested in performance as the is for a larger example and the ... 
[associations] [gathering]
 
asked by Craig Carter https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=12461 Score of 7
answered by lericr https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=84894 Score of 5
9.20.1.2 Highlight parts of two different curves

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=286272

In the plot generated by 
     y = 1; 
Plot[{Sin[x] x^-2/y, y}, {x, 0, 2}, PlotRange -> {0, 2}] 
 
how can one highlight the curve as shown below, and possibly fill ... 
[plotting] [plot-themes]
 
asked by User1729173 https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=88573 Score of 7
answered by Bob Hanlon https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=9362 Score of 10
9.20.1.3 DataStructure's "DynamicArray" underperforms Association?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=286320

The documentation for DynamicArray states that it is "An extensible array is useful for continuously appending elements, as well as for efficient element extraction and updating." 
I tried a ... 
[performance-tuning] [data-structures]
 
asked by Craig Carter https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=12461 Score of 7
9.20.1.4 How to recursively subdivide a quadrilateral?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=286394

I have the following problem which is most easily described by this diagram: 
 
We start off with a quadrilateral, not necessarily a square, with four fixed points, here represented in green. We have a ... 
[graphics] [mesh] [fractals]
 
asked by flinty https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=72682 Score of 6
answered by kglr https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=125 Score of 7
9.20.1.5 Better Stirling Approximation Error

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=286533

Stirling's Approximation is given by 
$$n! \sim \sqrt {2\pi n} \left ( \frac{n}{e}\right)^n$$ 
From a substantial improvement of the Stirling formula, we have an elegant approximation given by 
$$n! \sim ... 
[function-construction] [approximation]
 
asked by Moo https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=36141 Score of 5
answered by Daniel Huber https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=46318 Score of 3
9.20.1.6 IntervalMarkers bands not filled for negative x values

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=286507

Mathematica 13.2, I am trying to plot uncertain numbers using around, with  IntervalMarkers->"Bands"  so that these bands are filled. For negative x-axis ... 
[plotting]
 
asked by fernhughes https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=93187 Score of 5
answered by cvgmt https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=72111 Score of 3
9.20.1.7 How to set to 0 all terms in a matrix which contain a minus

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=286500

For a matrix like 
 F = {{ , x }, {-2 , -3 }}; 
F // MatrixForm 
 
I would like to set to 0 all terms  which contain a minus, in this case the bottom row, getting 
<... 
[list-manipulation] [matrix]
 
asked by florin https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=54979 Score of 5
answered by kglr https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=125 Score of 8