plot multiple lines according to size, shape, and alpha

[bjarthur]

see #1558 (comment)

plot(x=[1,2,3,1,2,3], y=[1,2,3,4,5,6], size=[1,1,1,2,2,2], Geom.line, Geom.point, Scale.size_discrete2(n->range(3pt, 8pt, length=n))) was:

and is now:

ditto for shape and alpha. so they now all act like color.

[codecov-commenter]

Codecov Report

Merging #1564 (141c9f4) into master (9245b75) will increase coverage by 0.84%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1564      +/-   ##
==========================================
+ Coverage   88.91%   89.76%   +0.84%     
==========================================
  Files          39       39              
  Lines        4636     4698      +62     
==========================================
+ Hits         4122     4217      +95     
+ Misses        514      481      -33     

Impacted Files	Coverage Δ
src/geom/line.jl	100.00% <100.00%> (ø)
src/varset.jl	97.82% <0.00%> (-2.18%)	⬇️
src/guide.jl	90.95% <0.00%> (+0.14%)	⬆️
src/misc.jl	65.64% <0.00%> (+0.61%)	⬆️
src/shapes.jl	100.00% <0.00%> (+0.78%)	⬆️
src/Gadfly.jl	76.62% <0.00%> (+0.98%)	⬆️
src/scale/scales.jl	93.40% <0.00%> (+1.09%)	⬆️
src/statistics.jl	95.60% <0.00%> (+1.15%)	⬆️
src/theme.jl	71.23% <0.00%> (+2.73%)	⬆️
src/geometry.jl	77.77% <0.00%> (+2.77%)	⬆️
... and 1 more

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[Mattriks]

See my #1558 (comment). I'm unconvinced by this PR. Linewidth is currently controlled by Theme(line_width), and should be developed into an aesthetic. alpha should change the line opacity, but needs to implemented yet. (https://discourse.julialang.org/t/gadfly-how-to-change-width-and-opacity-of-lines-in-geom-density/37823/4). The underlying issue is strokeopacity in Compose.jl

[bjarthur]

it's common to plot two lines with different shaped points. is that even possible in gadfly now?

[bjarthur]

to answer my own question: yes, but one must use layers, which seems cumbersome.

[Mattriks]

See my example plot in #1558 (using the group aesthetic).