Return to Answer

added 4 characters in body

Source Link

edited Jan 19, 2017 at 5:44

125.5k
11
407
581

If you have even more complicated expressions, you might want to use Heads -> True.

expr = {f, Subscript[g, i], h[i[j[a, b]]], s'[t] == u[t] + v[t]};

Union@Cases[exprUnion @ Cases[expr, Except[__Symbol?(Context@#Context @ # === "System`" &), _Symbol],
    {1, Infinity∞},
              Heads -> True]

{a, b, f, g, h, i, j, s, t, u, v}

Without checking heads:

Union@Cases[exprUnion @ Cases[expr, Except[__Symbol?(Context@#Context @ # === "System`" &), _Symbol], {1, Infinity∞}]

{a, b, f, g, i, t}

If you have even more complicated expressions, you might want to use Heads -> True.

expr = {f, Subscript[g, i], h[i[j[a, b]]], s'[t] == u[t] + v[t]};

Union@Cases[expr, Except[__Symbol?(Context@# === "System`" &), _Symbol],
    {1, Infinity}, Heads -> True]

{a, b, f, g, h, i, j, s, t, u, v}

Without checking heads:

Union@Cases[expr, Except[__Symbol?(Context@# === "System`" &), _Symbol], {1, Infinity}]

{a, b, f, g, i, t}

If you have even more complicated expressions, you might want to use Heads -> True.

expr = {f, Subscript[g, i], h[i[j[a, b]]], s'[t] == u[t] + v[t]};

Union @ Cases[expr, Except[__Symbol?(Context @ # === "System`" &), _Symbol], {1, ∞},
              Heads -> True]

{a, b, f, g, h, i, j, s, t, u, v}

Without checking heads:

Union @ Cases[expr, Except[__Symbol?(Context @ # === "System`" &), _Symbol], {1, ∞}]

{a, b, f, g, i, t}

Source Link

created Mar 13, 2013 at 21:49

István Zachar

47.2k
20
145
293

If you have even more complicated expressions, you might want to use Heads -> True.

expr = {f, Subscript[g, i], h[i[j[a, b]]], s'[t] == u[t] + v[t]};

Union@Cases[expr, Except[__Symbol?(Context@# === "System`" &), _Symbol],
    {1, Infinity}, Heads -> True]

{a, b, f, g, h, i, j, s, t, u, v}

Without checking heads:

Union@Cases[expr, Except[__Symbol?(Context@# === "System`" &), _Symbol], {1, Infinity}]

{a, b, f, g, i, t}