plotting - PlotLegends won't generate automatically more than 15 labels in v10

Update: NOT fixed in V10.0 - 12.0.0

While testing the examples from this recent post, i've noticed a problem in V.10 with PlotLegends when it has to automatically generate more than 15 labels (i.e. when there are more then 15 functions to plot). There's no problem with V.9.

The problem concerns the option values : Automatic and "Expressions". For example :

Plot[Evaluate[Range[20] + x], {x, -5, 5}, PlotLegends -> "Expressions"]

enter image description here

Plot[Evaluate[Range[20] + x], {x, -5, 5}, PlotLegends -> Automatic]

enter image description here

No problem however when you specify explicitly the labels in the legend :

Plot[Evaluate[Range[20] + x], {x, -5, 5}, PlotLegends -> Range[20]]

enter image description here

Answer

We may observe that the automatically generated legend limits the number of legend items to the number of available colors in the given color scheme. Using this utility function:

plot[scheme_] := Plot[Evaluate[Range[20] + x], {x, -5, 5},
   PlotLegends -> "Expressions", PlotStyle -> scheme]

Observe the result for indexed color scheme #42 which has only four colors:

plot[42]

enter image description here

There are eight in #26:

plot[26]

enter image description here

As since there are 21 in #60 all your lines have a legend:

plot[60]

enter image description here

And if you specify a gradient color scheme:

Plot[Evaluate[Range[50] + x], {x, -5, 5}, PlotLegends -> "Expressions", 
 PlotStyle -> "Rainbow"]

enter image description here

Comments

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