How to avoid plotting lines not defined in a Which function?

Question

fa1[x_] := Which[x >= 15, 1, x >= 10, 0.55, x >= 5, 0.1]
Plot[fa1[x], {x, -1, 20}, BaseStyle -> AbsoluteThickness[4], 
 PlotLegends -> 
  LineLegend["Expressions", BaseStyle -> AbsoluteThickness[4]]]

enter image description here

You can manually add exclusions, e.g., Exclusions->{10,15}, but I imagine you want a more generic solution? — ciao, Jul 06 '14 at 19:50
@rasher Thank you, it´s a good solution for me. It´s enough. — Mika Ike, Jul 06 '14 at 19:52
Specifically, fa1[x_] := Piecewise[{{1, x >= 15}, {0.55, x >= 10}, {0.1, x >= 5}}, Null] produces the desired plot without having to specify exclusions manually. — , Jul 06 '14 at 20:10
@RahulNarain Why don't you put this as an answer, so that I can upvote? Let other people decide if this is a duplicate or not. — eldo, Jul 06 '14 at 22:42
@RahulNarain Fantastic answer!. Your solution is perfect for me. I thougth that Piecewise and Which are diferent ways to make the same. — Mika Ike, Jul 07 '14 at 07:31

score 2 · Answer 1 · answered Jul 06 '14 at 20:08

2

You can post-process the plot to split the line into separate lines.

fa1[x_] := Which[x >= 15, 1, x >= 10, 0.55, x >= 5, 0.1]
plot = Plot[fa1[x], {x, -1, 20},
   BaseStyle -> AbsoluteThickness[4],
   PlotLegends -> LineLegend["Expressions",
     BaseStyle -> AbsoluteThickness[4]]];

linepos = Position[plot, Line];
a = Extract[plot, ReplacePart[First@linepos, -1 -> 1]];
b = Last /@ a;
c = Partition[b, 2, 1];
d = #1 == #2 & @@@ c;
e = DeleteCases[Split[d], {False}];
f = Length /@ e + 1;
g = # + {1, 0} & /@ Partition[Prepend[Accumulate[f], 0], 2, 1];
h = Take[a, #] & /@ g;
plot[[Sequence @@ ReplacePart[First@linepos, -1 -> 1]]] = h;

plot

enter image description here

answered Jul 06 '14 at 20:08

Chris Degnen

30,927
2
54
108

Thank you. It´s a solution, but I think that it´s a little complicate for a Mathematica user without huge knowledge of the software. I prefer use easier solutions. – Mika Ike Jul 07 '14 at 10:29
@MikaIke - yes, I would use Piecewise in retrospect. Nevertheless, sometimes editing the plot output is expedient. In this particular case there may be a shorter way to subdivide the line; I just took fairly basic steps. – Chris Degnen Jul 07 '14 at 12:14

How to avoid plotting lines not defined in a Which function?

1 Answers1