Feature request: link/share axes (like sharex in matplotlib or linkaxes in Matlab)

[pbouffard]

I have tried several backends that have interactive pan/zoom (PlotlyJS, PyPlot, InspectDR) and the link kwarg doesn't appear to have any effect in them. I'm not sure about the others but using PyPlot directly does work, e.g.:

julia> using PyPlot

julia> ax1=subplot(2,1,1)
PyObject <matplotlib.axes._subplots.AxesSubplot object at 0x12c6d6fd0>

julia> plot(randn(100,1))
1-element Array{PyCall.PyObject,1}:
 PyObject <matplotlib.lines.Line2D object at 0x139bb3dd0>

julia> ax2=subplot(2,1,2, sharex=ax1)
PyObject <matplotlib.axes._subplots.AxesSubplot object at 0x139c0fcd0>

julia> plot(randn(100,1))
1-element Array{PyCall.PyObject,1}:
 PyObject <matplotlib.lines.Line2D object at 0x139c49c90>

$ julia
               _
   _       _ _(_)_     |  A fresh approach to technical computing
  (_)     | (_) (_)    |  Documentation: https://docs.julialang.org
   _ _   _| |_  __ _   |  Type "?help" for help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 0.6.2 (2017-12-13 18:08 UTC)
 _/ |\__'_|_|_|\__'_|  |  Official http://julialang.org/ release
|__/                   |  x86_64-apple-darwin14.5.0

julia> Pkg.status()
28 required packages:
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125 additional packages:
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[apalugniok]

Seems to work for me, is this what you would expect?

using Plots
pyplot()
plot([rand(10) 100*rand(10)], layout = grid(1,2), link = :y)

[pbouffard]

@apalugniok That depends, when you pan or zoom one of the subplots with the mouse, does the other's y axis update so the y axes always match?

[apalugniok]

No it doesn't. Given the current implantation of link that I see this doesn't seem to be intended behavior, but unfortunately I can't say that for certain. This could be a nice feature to have for the interactive backends if they support it.

[pbouffard]

PyPlot supports it (see example above), and it looks like PlotlyJS should be able to: https://plot.ly/javascript/subplots/#subplots-with-shared-axes

[apalugniok]

Nice, thanks for the research! 😄 It'll come in handy!

[mkborregaard]

It should be possible and fairly simple in backends that support it natively (e.g. pyplot and plotlyjs) to check whether axes are linked then pass the appropriate keyword to the backend.

[apalugniok]

I don't think this is possible on Plotly, at least not the full functionality. The way Plotly "links" the axes is by attributing a series to another axis. You basically cannot have two truly separate x-axes linked to each other. Hopefully the example below makes sense of what I mean 😆

var trace1 = {
  x: [1, 2, 3],
  y: [4, 5, 6],
  type: 'scatter'
};

var trace2 = {
  x: [20, 30, 40],
  y: [50, 60, 70],
  xaxis: 'x2',
  yaxis: 'y2',
  type: 'scatter'
};

var data = [trace1, trace2];

var layout = {
  xaxis: {domain: [0, 0.45]},
  yaxis2: {anchor: 'x2'},
  xaxis2: {domain: [0.55, 1]}
};

Plotly.newPlot('myDiv', data, layout);

Attempting to link the two x-axes by switching the xaxis in trace2 to 'x' causes 'x2' to not exist anymore and breaks the desired layout (switching anchor in layout to 'x' doesn't fix this).

var trace1 = {
  x: [1, 2, 3],
  y: [4, 5, 6],
  type: 'scatter'
};

var trace2 = {
  x: [20, 30, 40],
  y: [50, 60, 70],
  xaxis: 'x',
  yaxis: 'y2',
  type: 'scatter'
};

var data = [trace1, trace2];

var layout = {
  xaxis: {domain: [0, 0.45]},
  yaxis2: {anchor: 'x2'},
  xaxis2: {domain: [0.55, 1]}
};

Plotly.newPlot('myDiv', data, layout);

[pbouffard]

@apalugniok I'm not sure where the problem is with your example as I haven't used Plotly directly in JavaScript before. But starting with their example (https://plot.ly/javascript/subplots/#subplots-with-shared-axes) and poking around a bit this is an MWE that has the functionality I'm looking for: https://codepen.io/anon/pen/yveXJo. Maybe the difference is having the plots stacked vertically instead of horizontally? If the latter wasn't possible that would be ok; for me at least the Nx1 subplots case with linked x axes is the most interesting.

[apalugniok]

So it does seem that link = :all wouldn't work for Plotly (works fine for PyPlot), but I think I managed to get Plotly to behave as you would like. I'd be great if you could checkout the PR and say what you think given I can't just post the picture of the results 😆.

[pbouffard]

@apalugniok I'd like to but am running into an error. This the the first time I've tried Pkg.checkout for anything other than a master branch so perhaps I'm doing something wrong:

julia> Pkg.checkout("Plots", "apalugniok:dynamic-link-axes")
INFO: Checking out Plots apalugniok:dynamic-link-axes...
ERROR: GitError(Code:EINVALIDSPEC, Class:Reference, Cannot locate local branch 'apalugniok:dynamic-link-axes')
Stacktrace:
 [1] lookup_branch(::Base.LibGit2.GitRepo, ::String, ::Bool) at ./libgit2/reference.jl:263
 [2] #branch!#86(::String, ::Bool, ::Bool, ::Function, ::Base.LibGit2.GitRepo, ::String, ::String) at ./libgit2/libgit2.jl:400
 [3] (::Base.LibGit2.#kw##branch!)(::Array{Any,1}, ::Base.LibGit2.#branch!, ::Base.LibGit2.GitRepo, ::String, ::String) at ./<missing>:0
 [4] (::Base.Pkg.Entry.##16#18{String,String,Bool,Bool})(::Base.LibGit2.GitRepo) at ./pkg/entry.jl:229
 [5] transact(::Base.Pkg.Entry.##16#18{String,String,Bool,Bool}, ::Base.LibGit2.GitRepo) at ./libgit2/libgit2.jl:882
 [6] with(::Base.Pkg.Entry.##15#17{String,String,Bool,Bool}, ::Base.LibGit2.GitRepo) at ./libgit2/types.jl:608
 [7] checkout(::String, ::String, ::Bool, ::Bool) at ./pkg/entry.jl:226
 [8] (::Base.Pkg.Dir.##4#7{Array{Any,1},Base.Pkg.Entry.#checkout,Tuple{String,String,Bool,Bool}})() at ./pkg/dir.jl:36
 [9] cd(::Base.Pkg.Dir.##4#7{Array{Any,1},Base.Pkg.Entry.#checkout,Tuple{String,String,Bool,Bool}}, ::String) at ./file.jl:70
 [10] #cd#1(::Array{Any,1}, ::Function, ::Function, ::String, ::Vararg{Any,N} where N) at ./pkg/dir.jl:36
 [11] #checkout#1(::Bool, ::Bool, ::Function, ::String, ::String) at ./pkg/pkg.jl:188
 [12] checkout(::String, ::String) at ./pkg/pkg.jl:188

[mkborregaard]

It's a little more complex than that, because the PR comes from @apalugniok 's local fork of Plots. You need to use git to set up his fork as a remote in your repo, then use git (also outside julia) to checkout the branch.

[apalugniok]

Here's a small demonstration I've put together.

using Plots; plotly()
l = @layout [  a{0.3w} [grid(3,3)
                         b{0.2h} ]]
plot(
    rand(10,11),
    layout = l, legend = false, seriestype = [:bar :scatter :path],
    title = ["($i)" for j = 1:1, i=1:11], titleloc = :right, titlefont = font(8),
    link = :both
)

[pbouffard]

Wow, do all those subplots get generated from just those lines of code?!? Very cool.

It might be a little while before I can find time to check the branch out and try this myself but based on the demo I think this is basically what I'm looking for and you should go ahead and merge if all else looks good.

Probably unrelated but I notice that when panning new tick labels for the revealed parts of the plot aren't drawn. Is that just a plotly thing (pretty sure matplotlib doesnt' behave that way) and if so a known issue?

Thanks for working this!

[apalugniok]

Yup! That code is all it takes 😄

The lack of ticks when panning is a Plots issue which also causes ticks not to be updated when zooming in (#1382).

[apalugniok]

Should be implemented by #1378!