Wolfram Language & System 11.0 (2016)|Legacy Documentation

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flattens out nested lists.

flattens to level n.

flattens subexpressions with head h.

flattens list by combining all levels sij to make each level i in the result.


  • Flatten "unravels" lists, effectively just deleting inner braces.
  • Flatten[list,n] effectively flattens the top level in list n times.
  • Flatten[f[e,]] flattens out subexpressions with head f.
  • If the mij are matrices, Flatten[{{m11,m12},{m21,m22}},{{1,3},{2,4}}] effectively constructs a single matrix from the "blocks" mij.
  • Flatten[list,{{i1},{i2},}] effectively transposes levels in list, putting level ik in list at level k in the result. Note that the function Transpose in effect uses an inverse of this specification.
  • Flatten flattens out levels in SparseArray objects just as in the corresponding ordinary arrays. »
Introduced in 1988
| Updated in 2007