# TreeCases TreeCases[tree,pattern]

gives a list of subtrees of tree with data matching pattern.

TreeCases[tree,pattern,levelspec]

gives a list of all subtrees of tree on levels specified by levelspec with data that matches the pattern.

TreeCases[tree,pattern,levelspec,n]

gives the first n subtrees in tree with data that matches the pattern.

TreeCases[pattern]

represents an operator form of TreeCases that can be applied to a tree.

# Details and Options • TreeCases lists the subtrees with data matching any pattern on any range of levels in a Tree object. The list of matches can be given in many different orders, including depth-first and breadth-first traversals.
• TreeCases[tree,pattern] tests all the subtrees of tree in turn to try to find ones with data that matches pattern.
• TreeCases uses standard level specifications as in TreeLevel:
•  n levels 1 through n All levels 0 through Infinity Infinity levels 1 through Infinity {n} level n only {n1,n2} levels n1 through n2
• The default value for levelspec in TreeCases is {0,Infinity}.
• TreeCases traverses subtrees in a left-to-right, depth-first order, with children visited before their parents.
• TreeCases[,TreeTraversalOrderorder] allows visiting subtrees in different orders, such as depth-first and breadth-first traversals.
• TreeCases[pattern][tree] is equivalent to TreeCases[tree,pattern].

# Examples

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## Basic Examples(4)

Find the subtrees whose data is an even number:

Find the inner subtrees whose data is an even number:

Find the first three subtrees whose data is a prime number:

Use the operator form of TreeCases:

## Scope(6)

Find the subtrees whose data is an odd integer:

Find the subtrees at levels 1 and 2 whose data is an odd integer:

Find the leaf subtrees whose data is an odd integer:

Find the inner subtrees whose data is an odd integer:

Find the first four subtrees whose data is an odd integer:

Use TreeCases as an operator form in a tree position specification:

## Options(3)

### TreeTraversalOrder(3)

By default, subtrees are listed in a depth-first order, with parents visited after their children:

Specify a top-down, right-to-left variant:

List subtrees in a breadth-first order, with nodes on the same level from the root visited before the nodes on the next level:

List subtrees in a leaves-first order, with nodes on the same level from the leaves visited before the nodes on the next level:

## Properties & Relations(5)

TreeCases extracts the positions given by TreePosition:

TreeCount gives the number of matching subtrees given by TreeCases:

TreeCases[tree,pattern,Infinity] is equivalent to TreeChildren@TreeExtract[tree,TreeCases[pattern]]:

Cases[expr,pattern,levelspec] is equivalent to TreeData/@TreeCases[ExpressionTree[expr,"Subexpressions"],pattern,levelspec]: