This is documentation for Mathematica 6, which was
based on an earlier version of the Wolfram Language.
View current documentation (Version 11.1)

Rearranging Nested Lists

You will encounter nested lists if you use matrices or generate multidimensional arrays and tables. Mathematica provides many functions for handling such lists.
Flatten[list]flatten out all levels in list
Flatten[list,n]flatten out the top n levels in list
Partition[list,{n1,n2,...}]partition into blocks of size n1×n2×...
Transpose[list]interchange the top two levels of lists
RotateLeft[list,{n1,n2,...}]rotate successive levels by ni places
PadLeft[list,{n1,n2,...}]pad successive levels to be length ni

A few functions for rearranging nested lists.

This "flattens out" sublists. You can think of it as effectively just removing all inner braces.
Click for copyable input
This flattens out only one level of sublists.
Click for copyable input
There are many other operations you can perform on nested lists. We will discuss more of them in "Manipulating Lists".