Is there a software where I can graph $D(x) \cdot \sin(x)\ \vert \ D(x) \text{ Dirichlet's function}$?
The problem is that it's a known function, and I haven't seen in Wolfram|Alpha, Desmos and Geogebra that it's recognized, and I've also not seen there the option to define graph a function that's defined in cases.
In the same sense that the graph of Dirichlet's function looks like the lines $y = 0$ and $y = 1$, with holes at every rational location in the lower line and holes at every irrational location in the upper, the graph $$ y = f(x) \chi_{\mathbf{Q}}(x) $$ looks like the graphs $y = 0$ and $y = f(x)$, with holes at every rational location in the line $y = 0$ and holes at every irrational location in the graph $y = f(x)$.