3D And 2D List To 1D List It converts lists like this:
To a list like this:
EDIT:
Found out flatten exists
KWRJGLERGIJBGW
What are 3D lists?
They are lsts inside of lists inside of lists etc. (I think).
How is that 3D?
I don't know. It just is.
There's a flatten function behind length
Huh, didn't know that existed. It was fun making the block though. 
That's a 1D list, not a 2D list.
1D list: {a b c d e f}
2D list: {{a b} {c d e} f}
3D list: {{a {b c}} {d {e f}}}
A 1D list is a list in which every item is an atom (something other than a list).
A 2D list is a list in which every item is an atom or a 1D list.
A 3D list is a list in which every item is an atom, a 1D list, or a 2D list.
The nonspecialist meaning of "dimension" as in space having three of them is related to the technical meaning. Think about how Snap! displays lists. A 1D list is shown as a single column of atomic items. But a 2D list is, by default, shown as a spreadsheet, in which every atomic value has a row and a column. Snap! isn't very good at showing 3D or higher dimensional lists; we display it as a spreadsheet (a table) in which the individual cells show the sprite input icon, which when clicked opens a view of the innards of that cell.
A list can have any number of dimensions. (In string theory they deal with 12-dimensional lists!) This idea of dimensions comes from linear algebra.
PS If the result you want is really a 1D list, just use 
.
Ohhhh, that makes since. Just like vision. 1D is one straight line, 2D is flat, 3D is shapes. (I'm having trouble thinking of ways to describe them ¯_(ツ)_/¯)
tsu
3D is solids.
i think they were trying to do a shrugging kaomoji
Well... I guess that is a kaomoji.