Manipulating lists

In-place functions are those that operate on lists or expressions directly. They have From or Into in their names (for example, Remove From and Insert Into). They do not return a result; you have to show the list to see the result. The first argument for an in-place function must be an L-value. An L-value is an entity such as a global variable whose value can be set.

myList = {a, b, c, d};

Insert Into( myList, 2, 3 );

Show( myList );

myList = {a, b, 2, c, d}

These examples show how to use Insert Into and Remove From with nested lists:

a = {{1, 2, 3}, {"A", "B", "C"}};

Show( a );

a = {{1, 2, 3}, {"A", "B", "C"}}

Insert Into( a[1], 99, 1 );

Show( a );

a = {{99, 1, 2, 3}, {"A", "B", "C"}}

Remove From( a[1], 1 );

Show( a );

a = {{1, 2, 3}, {"A", "B", "C"}}

Not in-place functions

For the not-in-place functions, you must either state the list directly or else quote a name that evaluates to a list. Such functions do not have From or Into in their names. They return manipulated lists or expressions without changing the original list or expression given in the first argument.

myNewList = Insert( {a, b, c, d}, 2, 3 );

{a, b, 2, c, d}

oldList = {a, b, c, d};

newList = Insert( oldList, 2, 3 );

{a, b, 2, c, d}

Substituting

Substitute() and Substitute Into() merit further discussion. Both functions find all matches to a pattern in a list (or expression) and replace them with another expression. Each pattern must be a name. The arguments are evaluated before they are applied, so most of the time you must quote them with an Expr() function.

Substitute( {a,b,c}, Expr( a ), 23); // returns {23,b,c}

Substitute( Expr( Sine( x ) ), Expr( x ), Expr( y ) ); // returns Sine(y)

To delay evaluating an argument, use NameExpr instead of Expr:

a = {quick, brown, fox, jumped, over, lazy, dogs};

b = Substitute( a, Expr( dogs ), Expr( cat ) );

canine = Expr( dogs );

equine = Expr( horse );

c = Substitute( a, Name Expr( canine ), Name Expr( equine ) );

Show( a, b, c );

a = {quick,brown,fox,jumped,over,lazy,dogs}

b = {quick,brown,fox,jumped,over,lazy,cat}

c = {quick,brown,fox,jumped,over,lazy,horse}