Returns the sub-expressions at a given level.
Level[expr, levelspec]
Level[expr, levelspec, f]
Level[{{a, b}, {c, d}}, {1}]
→ {{a, b}, {c, d}}Level[{{a, b}, {c, d}}, {2}]
→ {a, b, c, d}Level[Tree[1, {}], {-1}]
→ {Tree[1, {}]}Level[SparseArray[{1, 2}], {1}]
→ {}Head[First[Level[SparseArray[{1, 2}], {0}]]]
→ SparseArrayLevel[{{1, 2}, {3, {4, 5}}}, All]
→ {1, 2, {1, 2}, 3, 4, 5, {4, 5}, {3, {4, 5}}, {{1, 2}, {3, {4, 5}}}}