BUG: Setting 'array' tickmode on minor and major ticks causes 'ticksOut' to contain a duplicate of itself.

[ayjayt]

In cartesian/axes.js: calcTicks() we open a loop:

plotly.js/src/plots/cartesian/axes.js

Lines 927 to 929 in 8bf6d89

	// calc major first
	for(var major = 1; major >= (hasMinor ? 0 : 1); major--) {
	var isMinor = !major;

Where we eventually grab ticks using tickArray():

plotly.js/src/plots/cartesian/axes.js

Lines 947 to 958 in 8bf6d89

	// now that we've figured out the auto values for formatting
	// in case we're missing some ticktext, we can break out for array ticks
	if(mockAx.tickmode === 'array') {
	if(major) {
	tickVals = [];
	ticksOut = arrayTicks(ax);
	} else {
	minorTickVals = [];
	minorTicks = arrayTicks(ax);
	}
	continue;
	}

The problem is that arrayTicks(ax) always returns major AND minor ticks- So minorTicks and ticksOut will both contain all ticks. This is not the case were tickmode to be any other setting!

After we acquire the ticks, several hundred lines are dedicated to doing properties and checks dependent on whether we're major or minor- relevant lines concern setting major/minor ID and adjusting dates. This is where possible visual errors could be found, in these edge cases.

At the end, we concatenate minorTicks onto ticksOut right before return:

plotly.js/src/plots/cartesian/axes.js

Lines 1206 to 1208 in 8bf6d89

	}
	ticksOut = ticksOut.concat(minorTicks);

So we contain two sets of major ticks, two sets of minor ticks, each set the same. You can console.log() it to see.

This doesn't always propogate to the DOM: Since draw functions have to account for axes referring to the same items, they create a set stashed = {} and ensure not to redraw the same item twice. This would catch most errors.

I wanted to produce visual effects on edge cases, but date setting with arrays seems to be entirely wonky:

graph = Tabs.getGraph(); var update = {
    title: 'Mock: date_axes_period_breaks_automargin!',
    'xaxis.tickmode': 'array',
    'xaxis.tickvals': ["2015-4", "2015-5", "2015-6", "2015-7", "2015-8", "2015-9", "2015-10", "2015-11", "2015-12", "2016-1", "2016-2", "2016-3", "2016-4", "2016-5", "2016-6", "2016-7", "2016-8", "2016-9", "2016-10", "2016-11", "2016-12", "2017-1"],
    'xaxis.gridwidth': '2',
    'xaxis.ticklabelmode': "period",
};
Plotly.relayout(graph, update)

Pull request incoming.

[ayjayt]

Fixed!