# 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 • In TreeCases[tree,pattern], tree must be a valid Tree object.
• TreeCases[pattern][tree] is equivalent to TreeCases[tree,pattern].
• TreeCases uses standard level specifications:
•  n levels 1 through n 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}.
• A positive level n+1 consists of all subtrees of tree that are children of subtrees on level n.
• Level 0 corresponds to the root of the tree.
• Level -1 corresponds to the leaves.
• A negative level -(n+1) consists of all subtrees whose children are on levels -1, -2, , -n, with highest level -n.
• TreeCases traverses subtrees in a left-to-right, depth-first order, with children visited before their parents.

# Examples

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## Basic Examples(3)

Find the subtrees whose data is an even number:

Find the subtrees in the first level whose data is an even number:

Find the leaves whose data is an even number:

## Scope(6)

Find the subtrees whose data is an odd integer:

Find the subtrees at levels 0, 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 the operator form of TreeCases:

## Properties & Relations(2)

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

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