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Constructing Lists

Lists are widely used in the Wolfram Language, and there are many ways to construct them.

Range[n]the list {1,2,3,…,n}
Table[expr,{i,n}]the values of expr with i from 1 to n
Array[f,n]the list {f[1],f[2],…,f[n]}
NestList[f,x,n]{x,f[x],f[f[x]],…} with up to n nestings
Normal[SparseArray[{i1->v1,…},n]]a length n list with element ik being vk
Apply[List,f[e1,e2,…]]the list {e1,e2,…}

Some explicit ways to construct lists.

This gives a table of the first five powers of 2.
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Here is another way to get the same result.
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This gives a similar list.
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SparseArray lets you specify values at particular positions.
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You can also use patterns to specify values.
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Often you will know in advance how long a list is supposed to be, and how each of its elements should be generated. And often you may get one list from another.

Table[expr,{i,list}]the values of expr with i taking on values from list
Map[f,list]apply f to each element of list
MapIndexed[f,list]give f[elem,{i}] for the i^(th )element
Cases[list,form]give elements of list that match form
Select[list,test]select elements for which test[elem] is True
Pick[list,sel,form]pick out elements of list for which the corresponding elements of sel match form
TakeWhile[list,test]give elements ei from the beginning of list as long as test[ei] is True
list[[{i1,i2,…}]] or Part[list,{i1,i2,…}]
give a list of the specified parts of list

Constructing lists from other lists.

This selects elements less than 5.
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This takes elements up to the first element that is not less than 5.
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This explicitly gives numbered parts.
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This picks out elements indicated by a 1 in the second list.
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Sometimes you may want to accumulate a list of results during the execution of a program. You can do this using Sow and Reap.

Sow[val]sow the value val for the nearest enclosing Reap
Reap[expr]evaluate expr, returning also a list of values sown by Sow

Using Sow and Reap.

This program iteratively squares a number.
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This does the same computation, but accumulating a list of intermediate results above 1000.
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An alternative but less efficient approach involves introducing a temporary variable, then starting with t={}, and successively using AppendTo[t,elem].

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