Re: jitter documentation

[Allin C. <cot...@wf...>]

On Thu, 15 Oct 2020, Ethan A Merritt wrote:

> On Thursday, 15 October 2020 08:02:27 PDT Allin Cottrell wrote:
>> Maybe I'm missing something, but isn't the documentation for
>> "jitter" backwards with respect to the swarm/square choice?
>>
>> The text reads thus: "The default jittering operation displaces
>> points only along x. This produces a distinctive pattern sometimes
>> called a "bee swarm plot". The optional keyword square adjusts the y
>> coordinate of displaced points in addition to their x coordinate so
>> that the points lie in distinct layers..."
>
> The text is correct as written.  Perhaps the attached figure,
> combining two plots from jitter.dem, will clarify.
>
> Left panel:
> 	original data, randomly distributed on y, all x values the same
> Center panel:
> 	"beeswarm" result from displacing points along x
> 	if they would otherwise overlap.
> 	Points are still randomly distributed on y.
> Right panel:
> 	"square" plot uses the x displacements that would
> 	generate a beeswarm plot, and adds an y displacement
> 	that is effectively a floor(y) operation where the unit of
> 	the floor operation is the "overlap" parameter to jitter.
>
>>
>> In the demo and in my own usage it seems the default is in fact to
>> displace in both the x and y dimensions while "square" limits the
>> scatter to the x dimension. (Except that in some cases I'm not
>> getting any y displacement with either choice, but that's another
>> issue.)

Thanks, Ethan. I think I get it now. But this is potentially quite 
confusing -- to understand exactly what jitter is doing one really 
has to look closely at the y data in numerical form. So 'swarm' 
preserves the original y values and just shoves points sideways to 
get them off each other, while 'square' will also regularize the y 
values to get the points into straight rows (more or less).

And then, given a pile-up of data points at some discrete {x,y}
value, there's no option to nudge them apart in both dimensions to 
form a cloud? I had the idea that was what "bee swarm" was about, 
but I guess I was mistaken.

--
Allin Cottrell
Department of Economics
Wake Forest University